Steps to reproduce:

1. I open a DCC Whiteboard connection to myself on a connection to psyBNC connected to an IRC network

2. I get both the DCC Whiteboard tab (in the background, Focus New Tabs is off) and a query by "-psyBNC" with the  following text:

"[19:05] <-psyBNC> Sho sent a DCC Chat Request. Use /DCCANSWER Sho or /DCCANSWER S=Sho (SSL) to establish the connection (<ip>/1026)."

3. I switch to the DCC Whiteboard tab.

4. I switch to the query tab and do /DCCANSWER Sho.

5. The sequence of events in 3 and 4 cause the remember line to be inserted into the Whiteboard tab followed by "/DCCANSWER Sho" (standard marker line settings: insert on hide, but only on text append).

6. I do "Clear Marker Lines" and get a hang. Attach gdb and bt:

#0  0x0000003eb5e3acda in QTextBlock::length (this=0x7fff0c8431c0) at text/qtextobject.cpp:1029
#1  0x0000003eb5e7ca38 in QTextCursor::select (this=0x7fff0c843210, selection=QTextCursor::BlockUnderCursor) at text/qtextcursor.cpp:1563
#2  0x0000000000550fec in IRCView::voidLineBlock (this=0x2909b00, rem=...) at /home/sho/devel/src/konversation/src/viewer/ircview.cpp:487
#3  0x0000000000551042 in IRCView::clearLines (this=0x2909b00) at /home/sho/devel/src/konversation/src/viewer/ircview.cpp:496
#4  0x0000000000573426 in ViewContainer::clearViewLines (this=0xa58e30) at /home/sho/devel/src/konversation/src/viewer/viewcontainer.cpp:2044
#5  0x00000000005760f7 in ViewContainer::qt_static_metacall (_o=0xa58e30, _c=QMetaObject::InvokeMetaMethod, _id=55, _a=0x7fff0c843480) at /home/sho/devel/build/konversation/src/viewcontainer.moc:333
#6  0x00000031f678d571 in QMetaObject::activate (sender=0xdc7e80, m=<optimized out>, local_signal_index=<optimized out>, argv=0x7fff0c843480) at kernel/qobject.cpp:3547
#7  0x0000003eb5bc39e2 in QAction::triggered (this=<optimized out>, _t1=false) at .moc/release-shared/moc_qaction.cpp:276
#8  0x0000003eb5bc3bcf in QAction::activate (this=0xdc7e80, event=<optimized out>) at kernel/qaction.cpp:1257
#9  0x0000003eb600bbe9 in QMenuPrivate::activateCausedStack (this=0xe791c0, causedStack=..., action=0xdc7e80, action_e=QAction::Trigger, self=true) at widgets/qmenu.cpp:1028
#10 0x0000003eb6011d32 in QMenuPrivate::activateAction (this=0xe791c0, action=0xdc7e80, action_e=QAction::Trigger, self=true) at widgets/qmenu.cpp:1120
#11 0x0000003eb73131a0 in KMenu::mouseReleaseEvent (this=0xe85df0, e=0x7fff0c844050) at /usr/src/debug/kdelibs-4.8.2/kdeui/widgets/kmenu.cpp:464
#12 0x0000003eb5c1a0da in QWidget::event (this=0xe85df0, event=0x7fff0c844050) at kernel/qwidget.cpp:8362
#13 0x0000003eb60132cb in QMenu::event (this=0xe85df0, e=0x7fff0c844050) at widgets/qmenu.cpp:2469
#14 0x0000003eb5bc9bc4 in notify_helper (e=0x7fff0c844050, receiver=0xe85df0, this=0xa2ea80) at kernel/qapplication.cpp:4554
#15 QApplicationPrivate::notify_helper (this=0xa2ea80, receiver=0xe85df0, e=0x7fff0c844050) at kernel/qapplication.cpp:4526
#16 0x0000003eb5bcf313 in QApplication::notify (this=<optimized out>, receiver=0xe85df0, e=0x7fff0c844050) at kernel/qapplication.cpp:4097
#17 0x0000003eb7251f96 in KApplication::notify (this=0x7fff0c844d60, receiver=0xe85df0, event=0x7fff0c844050) at /usr/src/debug/kdelibs-4.8.2/kdeui/kernel/kapplication.cpp:311
#18 0x00000031f67798dc in QCoreApplication::notifyInternal (this=0x7fff0c844d60, receiver=0xe85df0, event=0x7fff0c844050) at kernel/qcoreapplication.cpp:876
#19 0x0000003eb5bcab92 in sendEvent (event=<optimized out>, receiver=<optimized out>) at ../../src/corelib/kernel/qcoreapplication.h:231
#20 QApplicationPrivate::sendMouseEvent (receiver=0xe85df0, event=0x7fff0c844050, alienWidget=0x0, nativeWidget=0xe85df0, buttonDown=0x0, lastMouseReceiver=..., spontaneous=true)
    at kernel/qapplication.cpp:3165
#21 0x0000003eb5c46a61 in QETWidget::translateMouseEvent (this=0xe85df0, event=<optimized out>) at kernel/qapplication_x11.cpp:4457
#22 0x0000003eb5c4525a in QApplication::x11ProcessEvent (this=0x7fff0c844d60, event=0x7fff0c844910) at kernel/qapplication_x11.cpp:3646
#23 0x0000003eb5c6cbdc in x11EventSourceDispatch (s=0xa3c750, callback=0, user_data=0x0) at kernel/qguieventdispatcher_glib.cpp:148
#24 0x0000003b38c44f3d in g_main_context_dispatch () from /lib64/libglib-2.0.so.0
#25 0x0000003b38c45738 in ?? () from /lib64/libglib-2.0.so.0
#26 0x0000003b38c4590c in g_main_context_iteration () from /lib64/libglib-2.0.so.0
#27 0x00000031f67a85bf in QEventDispatcherGlib::processEvents (this=0x9ce330, flags=<optimized out>) at kernel/qeventdispatcher_glib.cpp:424
#28 0x0000003eb5c6c8ce in QGuiEventDispatcherGlib::processEvents (this=<optimized out>, flags=<optimized out>) at kernel/qguieventdispatcher_glib.cpp:207
#29 0x00000031f6778a12 in QEventLoop::processEvents (this=<optimized out>, flags=...) at kernel/qeventloop.cpp:149
#30 0x00000031f6778c67 in QEventLoop::exec (this=0x7fff0c844ce0, flags=...) at kernel/qeventloop.cpp:204
#31 0x00000031f677d665 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:1148
#32 0x000000000047a4da in main (argc=5, argv=0x7fff0c845c08) at /home/sho/devel/src/konversation/src/main.cpp:123