Tab completion is broken again in the Sage backend.
Using Cantor 0.5 (it's not possible to choose it in the version field), Sage 6.0

Reproducible: Always

Steps to Reproduce:
1.Start a new Sage session
2.Evaluate "a=5"
3.Type "a."+(tab)
Actual Results:  
No completions 

Expected Results:  
List of completions

From the debug output, the completions list is retrieved correctly from the backend, but not displayed:

cantor(29735) WorksheetTextItem::sceneEvent: ShortcutOverride 16777217 QFlags()
cantor(29735) SageSession::evaluateExpression: evaluating:  "__cantor_enable_typesetting(false)"
cantor(29735) SageExpression::SageExpression:
cantor(29735) SageExpression::evaluate: evaluating  "__cantor_enable_typesetting(false)"
cantor(29735) CantorPart::worksheetStatusChanged: wsStatusChange 0
cantor(29735) SageSession::runFirstExpression: writing  "__cantor_enable_typesetting(false)"  to the process
cantor(29735) SageSession::evaluateExpression: evaluating:  "__hist_tmp__=_; __CANTOR_IPYTHON_SHELL__.complete("a.");_=__hist_tmp__"
cantor(29735) SageExpression::SageExpression:
cantor(29735) SageExpression::evaluate: evaluating  "__hist_tmp__=_; __CANTOR_IPYTHON_SHELL__.complete("a.");_=__hist_tmp__"
cantor(29735) SageSession::evaluateExpression: evaluating:  "__cantor_enable_typesetting(true)"
cantor(29735) SageExpression::SageExpression:
cantor(29735) SageExpression::evaluate: evaluating  "__cantor_enable_typesetting(true)"
cantor(29735) SageSession::readStdOut: out:  "sage: sage: "
cantor(29735) SageExpression::parseOutput: got prompt 0    -1
cantor(29735) SageExpression::parseOutput: got prompt 0    -1
cantor(29735) SageExpression::evalFinished: evaluation finished
cantor(29735) SageExpression::evalFinished: ""
cantor(29735) Cantor::Expression::setResult: settting result to a type  1  result
cantor(29735) SageSession::runFirstExpression: writing  "__hist_tmp__=_; __CANTOR_IPYTHON_SHELL__.complete("a.");_=__hist_tmp__"  to the process
cantor(29735) SageSession::readStdOut: out:  "('a.',
 ['a.N',
  'a.abs',
  'a.additive_order',
  'a.base_extend',
  'a.base_ring',
  'a.binary',
"
cantor(29735) SageSession::readStdOut: out:  "  'a.binomial',
  'a.bits',
  'a.cartesian_product',
  'a.category',
  'a.ceil',
  'a.conjugate',
  'a.coprime_integers',
  'a.crt',
  'a.db',
  'a.degree',
  'a.denominator',
  'a.digits',
  'a.divide_knowing_divisible_by',
  'a.divides',
  'a.divisors',
  'a.dump',
  'a.dumps',
  'a.exact_log',
  'a.exp',
  'a.factor',
  'a.factorial',
  'a.floor',
  'a.gamma',
  'a.gcd',
  'a.global_height',
"
cantor(29735) SageSession::readStdOut: out:  "  'a.imag',
  'a.inverse_mod',
  'a.inverse_of_unit',
  'a.is_idempotent',
  'a.is_integral',
  'a.is_irreducible',
  'a.is_nilpotent',
  'a.is_norm',
  'a.is_one',
  'a.is_perfect_power',
  'a.is_power',
  'a.is_power_of',
  'a.is_prime',
"
cantor(29735) SageSession::readStdOut: out:  "  'a.is_prime_power',
  'a.is_pseudoprime',
  'a.is_square',
  'a.is_squarefree',
  'a.is_unit',
  'a.is_zero',
  'a.isqrt',
  'a.jacobi',"
cantor(29735) SageSession::readStdOut: out:  "
  'a.kronecker',
  'a.lcm',
  'a.leading_coefficient',
  'a.list',
  'a.log',
  'a.mod',
"
cantor(29735) SageSession::readStdOut: out:  "  'a.multifactorial',
  'a.multiplicative_order',
  'a.n',
  'a.nbits',
  'a.ndigits',
"
cantor(29735) SageSession::readStdOut: out:  "  'a.next_prime',
  'a.next_probable_prime',
  'a.nth_root',
  'a.numerator',
  'a.numerical_approx',"
cantor(29735) SageSession::readStdOut: out:  "
  'a.odd_part',
  'a.ord',
  'a.order',
  'a.ordinal_str',
"
cantor(29735) SageSession::readStdOut: out:  "  'a.parent',
  'a.perfect_power',
  'a.popcount',
  'a.powermod',
  'a.powermodm_ui',
"
cantor(29735) SageSession::readStdOut: out:  "  'a.prime_divisors',
  'a.prime_factors',
  'a.prime_to_m_part',
  'a.quo_rem',
"
cantor(29735) SageSession::readStdOut: out:  "  'a.radical',
  'a.rational_reconstruction',
  'a.real',
  'a.rename',
  'a.reset_name',
  'a.save',"
cantor(29735) SageSession::readStdOut: out:  "
  'a.sign',
  'a.sqrt',
  'a.sqrt_approx',
  'a.sqrtrem',
  'a.squarefree_part',
"
cantor(29735) SageSession::readStdOut: out:  "  'a.str',
  'a.subs',
  'a.substitute',
  'a.support',
  'a.test_bit',"
cantor(29735) SageSession::readStdOut: out:  "
  'a.trailing_zero_bits',
  'a.trial_division',
  'a.val_unit',
  'a.valuation',
"
cantor(29735) SageSession::readStdOut: out:  "  'a.version',
  'a.xgcd'])
"
cantor(29735) SageSession::readStdOut: out:  "sage: "
cantor(29735) SageExpression::parseOutput: got prompt 0    -1
cantor(29735) SageSession::readStdOut: out:  "sage: "
cantor(29735) SageExpression::parseOutput: got prompt 0    -1
cantor(29735) SageExpression::evalFinished: evaluation finished
cantor(29735) SageExpression::evalFinished: "('a.',
 ['a.N',
  'a.abs',
  'a.additive_order',
  'a.base_extend',
  'a.base_ring',
  'a.binary',
  'a.binomial',
  'a.bits',
  'a.cartesian_product',
  'a.category',
  'a.ceil',
  'a.conjugate',
  'a.coprime_integers',
  'a.crt',
  'a.db',
  'a.degree',
  'a.denominator',
  'a.digits',
  'a.divide_knowing_divisible_by',
  'a.divides',
  'a.divisors',
  'a.dump',
  'a.dumps',
  'a.exact_log',
  'a.exp',
  'a.factor',
  'a.factorial',
  'a.floor',
  'a.gamma',
  'a.gcd',
  'a.global_height',
  'a.imag',
  'a.inverse_mod',
  'a.inverse_of_unit',
  'a.is_idempotent',
  'a.is_integral',
  'a.is_irreducible',
  'a.is_nilpotent',
  'a.is_norm',
  'a.is_one',
  'a.is_perfect_power',
  'a.is_power',
  'a.is_power_of',
  'a.is_prime',
  'a.is_prime_power',
  'a.is_pseudoprime',
  'a.is_square',
  'a.is_squarefree',
  'a.is_unit',
  'a.is_zero',
  'a.isqrt',
  'a.jacobi',
  'a.kronecker',
  'a.lcm',
  'a.leading_coefficient',
  'a.list',
  'a.log',
  'a.mod',
  'a.multifactorial',
  'a.multiplicative_order',
  'a.n',
  'a.nbits',
  'a.ndigits',
  'a.next_prime',
  'a.next_probable_prime',
  'a.nth_root',
  'a.numerator',
  'a.numerical_approx',
  'a.odd_part',
  'a.ord',
  'a.order',
  'a.ordinal_str',
  'a.parent',
  'a.perfect_power',
  'a.popcount',
  'a.powermod',
  'a.powermodm_ui',
  'a.prime_divisors',
  'a.prime_factors',
  'a.prime_to_m_part',
  'a.quo_rem',
  'a.radical',
  'a.rational_reconstruction',
  'a.real',
  'a.rename',
  'a.reset_name',
  'a.save',
  'a.sign',
  'a.sqrt',
  'a.sqrt_approx',
  'a.sqrtrem',
  'a.squarefree_part',
  'a.str',
  'a.subs',
  'a.substitute',
  'a.support',
  'a.test_bit',
  'a.trailing_zero_bits',
  'a.trial_division',
  'a.val_unit',
  'a.valuation',
  'a.version',
  'a.xgcd'])"
cantor(29735) Cantor::Expression::setResult: settting result to a type  1  result
cantor(29735) CommandEntry::showCompletions: completion:  "a."
cantor(29735) CommandEntry::showCompletions: showing  ("a.")
cantor(29735) CommandEntry::completeCommandTo: completion:  "a."
cantor(29735) SageSession::runFirstExpression: writing  "__cantor_enable_typesetting(true)"  to the process
cantor(29735) SageSession::evaluateExpression: evaluating:  "__cantor_internal__ = _; type(a.); _ = __cantor_internal__"
cantor(29735) SageExpression::SageExpression:
cantor(29735) SageExpression::evaluate: evaluating  "__cantor_internal__ = _; type(a.); _ = __cantor_internal__"
cantor(29735) SageSession::readStdOut: out:  "sage: sage: "
cantor(29735) SageExpression::parseOutput: got prompt 0    -1
cantor(29735) SageExpression::parseOutput: got prompt 0    -1
cantor(29735) SageExpression::evalFinished: evaluation finished
cantor(29735) SageExpression::evalFinished: ""
cantor(29735) Cantor::Expression::setResult: settting result to a type  1  result
cantor(29735) SageSession::runFirstExpression: writing  "__cantor_internal__ = _; type(a.); _ = __cantor_internal__"  to the process
cantor(29735) SageSession::readStdOut: out:  "  File "<ipython-input-69-939d09e23660>", line 1
    __cantor_internal__ = _; type(a.); _ = __cantor_internal__
                                    ^
SyntaxError: invalid syntax

"
cantor(29735) SageSession::readStdOut: out:  "sage: "
cantor(29735) SageExpression::parseOutput: got prompt 0    -1
cantor(29735) SageSession::readStdOut: out:  "sage: "
cantor(29735) SageExpression::parseOutput: got prompt 0    -1
cantor(29735) SageExpression::evalFinished: evaluation finished
cantor(29735) SageExpression::evalFinished: "File "<ipython-input-69-939d09e23660>", line 1
    __cantor_internal__ = _; type(a.); _ = __cantor_internal__
                                    ^
SyntaxError: invalid syntax"
cantor(29735) Cantor::Expression::setResult: settting result to a type  1  result
cantor(29735) CommandEntry::completeLineTo: line completion:  "a."
cantor(29735) CantorPart::worksheetStatusChanged: wsStatusChange 1