The discussion at https://bugreports.qt-project.org/browse/QTCREATORBUG-9010 came to the conclusion that the XK_ISO_Level5_Shift key is missing in KeyTbl in qtbase/src/plugins/platforms/xcb/qxcbkeyboard.cpp.
This key is used by some alternative keyboard layouts like the german NEO layout.
The following QKeyEvent is generated on key press:
key code: -1 / 0xFFFFFFFFFFFFFFFF
text: empty string
nativeScancode: 108 / 0x6C
nativeVirtualKey: 65041 / 0xFE11
The Qt Creator FakeVim plugin doesn't ignore -1 keycodes and interprets the keystroke as 'ÿ'. I also suspect this to be the cause of KDE programs not accepting keyboard shortcuts containing this meta key, and Kate exiting the visual selection in vim mode when this meta key is pressed.