Global Menu disappearing after switching to Forms in KDE

Steps to reproduce:

1. Have latest KDE
2. Have Global Menu widget that integrates application menu into panel
3. Open Qt Creator through terminal and create a new project or open an existing one
4. Open any Source file
5. Open any Form file
6. Switch to another window or show the desktop in KDE and then go back to Qt Creator
7. Menu disappeared completely and can't even be accessed through "Alt + F" combination
8. SOFT ASSERT warning in terminal output

SOFT ASSERT: "index" in file /work/build/qt-creator/src/plugins/coreplugin/editortoolbar.cpp, line 412

Seems like it's not a KDE issue. Checking other apps based on Qt (both 4 and 5 versions) gave normal results (menu is not disappearing).

PS: The workaround for now is just not use the KDE Global Menu or have a KDE activity without Global Menu.