This is konsole @ git revision 9f8d3933940744cf8eca50d57558bfac82eb0ee7. Pressing Ctrl+Space works just fine, as does Alt+Space. However, pressing Ctrl+Alt+Space sends the same keycode(s) as Ctrl+Space does. I'm pretty sure that the konsole in KDE 4.x did not have this limitation, and yes, there are applications that use this combination (Emacs for mark-sexp). Running »cat« shows the following: - for Ctrl+Space: ^@ - for Alt+Space: ^[ (with a trailing space) - for Ctrl+Alt+Space: ^@ Reproducible: Always Steps to Reproduce: 1. Run »emacs -nw« in konsole 2. Press Ctrl+Alt+Space 3. Emacs will show the message "mark set" instead of actually marking the sexp at point. Actual Results: See description for all the details.
In Emacs there's a secondary key binding for mark-sexp: Ctrl+Alt+@. This doesn't work in current konsole either. I've re-installed konsole from KDE 4.14.6, and both combinations (Ctrl+Alt+Space and Ctrl+Alt+@) work just fine there. Seems to be a general problem, not just with a single combination (and Ctrl+Space was fixed only three commits ago itself…).
You can fine tune the escape sequences sent by key combos using the konsole key bindings editor. Did you try that?
For me, Ctrl+Alt+Space generates ^[^@ (that is, 0x1B 0x00) in konsole 17.04.3, just as in xterm and vte. I guess the bug's been fixed since it was reported.
Indeed it's been fixed. Thanks. Feel free to reopen if you can still reproduce this issue.