Problem with typing Shift+<russian Л> in SynEdit

[AlexTP]

I am getting the user bugreport. He has Ubuntu 23.10, and Double Commander Qt5 version installed (last from https://sourceforge.net/p/doublecmd/wiki/Download/ ).

When he types Shift+Л in internal editor, app wants to close the editor and asks "Save file?".
Other russian letters are working OK.

Qt5: last official package.
libQt5Pas: version 2.15 from David Bannon.

[Martin_fr]

And the question is about
- This is a Linux issue (i.e. fine on other platforms)
- This is a QT issue (i.e. fine on gtk)
- This is an IDE issue (i.e fine with stand alone synedit)
- ....

What scan-code VK_... is that key producing (with / without shift).
- Is the scan code correct?
- If yes, and if it is an IDE issue, check the keymapping.

[AlexTP]

- This is a Ubuntu 23.10 issue, but works good on Ubuntu 22.04
- All ok on gtk2
- This is not the IDE issue, because user tried to run my small demo (attached) and he saw the same problem: Л is entered only after 2 keypresses. This is TCustomControl issue (visible on SynEdit and ATSynEdit), a OnKeyPress issue.
- This is with Ubuntu detault package libqt5Pas

[zeljko]

Please open an issue against qt5/qt6 widgetsets, attach simple example program (without 3rd party components) and howto reproduce (and what distro and window manager need to be installed to reproduce it. Also, wayland or x11 if it's linux).

[AlexTP]

Submitted: https://gitlab.com/freepascal.org/lazarus/lazarus/-/issues/40641