I am seeing a crash when using Qt4 of SHA d5d0ecab with Qt Creator.
This crash does NOT happen when using Qt4 with SHA 5fd483d0 with the same binaries of Qt Creator.

I can reproduce this crash by selecting a area of text and then hitting backspace or delete.

Example line (from Qt Creator's baseqtversion.cpp):
QtVersionNumber::QtVersionNumber(int ma, int mi, int p)

Selecting from the second Q to the end of line: no crash.
Selecting from the second Q to the 4th r: no crash
Selecting from the first Q to the end of line: no crash.
Selecting from the second t to the end of line: CRASH.
Selecting from the second t to the 3rd i: CRASH
Selecting from the second t to the (: no crash

All examples have the letters given as part of the selection.

This is the backtrace:

0 raise /usr/lib/libc.so.6 0x7ffff502ffa5
1 abort /usr/lib/libc.so.6 0x7ffff5031428
2 qt_message_output qglobal.cpp 2266 0x7ffff5e72df3
3 qt_message(QtMsgType, const char *, typedef __va_list_tag __va_list_tag *) qglobal.cpp 2312 0x7ffff5e72f6f
4 qFatal qglobal.cpp 2495 0x7ffff5e73692
5 qt_assert_x qglobal.cpp 2021 0x7ffff5e729eb
6 QVarLengthArray<int, 16>::remove qvarlengtharray.h 319 0x7ffff6c921e5
7 QTextEngine::resolveAdditionalFormats qtextengine.cpp 2855 0x7ffff6c8cdf7
8 QTextEngine::itemize qtextengine.cpp 1633 0x7ffff6c870b0
9 QTextLayout::beginLayout qtextlayout.cpp 624 0x7ffff6c94d00
10 QPlainTextDocumentLayout::layoutBlock qplaintextedit.cpp 373 0x7ffff6f72596
11 QPlainTextDocumentLayout::documentChanged qplaintextedit.cpp 303 0x7ffff6f71f9b
12 QTextDocumentPrivate::finishEdit qtextdocument_p.cpp 1220 0x7ffff6ccc90c
13 QTextDocumentPrivate::endEditBlock qtextdocument_p.cpp 1201 0x7ffff6ccc790
14 QTextCursor::removeSelectedText qtextcursor.cpp 1662 0x7ffff6d0001a
15 QTextCursor::deleteChar qtextcursor.cpp 1500 0x7ffff6cff813
16 QTextControlPrivate::keyPressEvent qtextcontrol.cpp 1269 0x7ffff6c73597
17 QTextControl::processEvent qtextcontrol.cpp 946 0x7ffff6c717e3
18 QTextControl::processEvent qtextcontrol.cpp 906 0x7ffff6c7168e
19 QPlainTextEditPrivate::sendControlEvent qplaintextedit_p.h 136 0x7ffff6f7ce5d
20 QPlainTextEdit::keyPressEvent qplaintextedit.cpp 1698 0x7ffff6f781d2
21 TextEditor::BaseTextEditorWidget::keyPressEvent basetexteditor.cpp 1857 0x7fffebdda76e
22 CppEditor::Internal::CPPEditorWidget::keyPressEvent cppeditor.cpp 1644 0x7fffe7ebd5c9
23 QWidget::event qwidget.cpp 8406 0x7ffff69dbbf8
24 QFrame::event qframe.cpp 557 0x7ffff6ea5c7b
25 QAbstractScrollArea::event qabstractscrollarea.cpp 996 0x7ffff6f4eb1e
26 QPlainTextEdit::event qplaintextedit.cpp 1520 0x7ffff6f777a2
27 TextEditor::BaseTextEditorWidget::event basetexteditor.cpp 2115 0x7fffebddbfd7
28 CppEditor::Internal::CPPEditorWidget::event cppeditor.cpp 1578 0x7fffe7ebcde2
29 QApplicationPrivate::notify_helper qapplication.cpp 4557 0x7ffff6978e28
30 QApplication::notify qapplication.cpp 3998 0x7ffff69766eb
31 QCoreApplication::notifyInternal qcoreapplication.cpp 915 0x7ffff5fb9f82
32 QCoreApplication::sendSpontaneousEvent qcoreapplication.h 234 0x7ffff697c235
33 qt_sendSpontaneousEvent qapplication.cpp 5555 0x7ffff697916b
34 QKeyMapper::sendKeyEvent qkeymapper_x11.cpp 1866 0x7ffff6a4dc60
35 QKeyMapperPrivate::translateKeyEvent qkeymapper_x11.cpp 1836 0x7ffff6a4d96f
36 QApplication::x11ProcessEvent qapplication_x11.cpp 3523 0x7ffff6a14842
37 x11EventSourceDispatch qguieventdispatcher_glib.cpp 146 0x7ffff6a4fe80
38 g_main_context_dispatch /usr/lib/libglib-2.0.so.0 0x7ffff4740475
39 ?? /usr/lib/libglib-2.0.so.0 0x7ffff47407a8
40 g_main_context_iteration /usr/lib/libglib-2.0.so.0 0x7ffff4740864
41 QEventDispatcherGlib::processEvents qeventdispatcher_glib.cpp 424 0x7ffff5ff5b9f
42 QGuiEventDispatcherGlib::processEvents qguieventdispatcher_glib.cpp 204 0x7ffff6a5022e
43 QEventLoop::processEvents qeventloop.cpp 149 0x7ffff5fb7398
44 QEventLoop::exec qeventloop.cpp 204 0x7ffff5fb752c
45 QCoreApplication::exec qcoreapplication.cpp 1187 0x7ffff5fba618
46 QApplication::exec qapplication.cpp 3818 0x7ffff697607e
47 main main.cpp 435 0x40b952