Bug 451120

Summary: shortcuts for switching keyboard layout change normal shortcuts behavior
Product: [Applications] systemsettings Reporter: skrachen <j.chataignon>
Component: kcm_keyboardAssignee: Plasma Bugs List <plasma-bugs-null>
Status: RESOLVED UPSTREAM    
Severity: normal CC: butirsky, nate
Priority: NOR    
Version First Reported In: 5.24.2   
Target Milestone: ---   
Platform: Manjaro   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:

Description skrachen 2022-03-04 07:27:12 UTC 
SUMMARY
Setting Left Ctrl + Left Shift as shortcut for switching keyboard layout changes the normal behavior of Left Ctrl + Left Shift + other keys. For example, in a text editor Ctrl+Shift+arrowLeft should select the word on the left of the cursor, but now it just moves the cursor to the left of the word. Ctrl+Shift+T in a browser should re-open the last closed tab, but just opens a new tab (like Ctrl+T does).
(Only tested under Xorg, not Wayland)

STEPS TO REPRODUCE
1. Go to Settings > Hardware > Input Devices > Keyboard > Layouts
2. In Shortcuts for Switching Layouts > Main shortcuts, select Left Ctrl + Left Shift
3. Try using any shortcut comprising Ctrl+Shift+[another key]

OBSERVED RESULT
Pressing Ctrl+Shift+[some key] behaves like Ctrl+[some key], as if Shift wasn't pressed

EXPECTED RESULT
normal keyboard behavior

SOFTWARE/OS VERSIONS
Kernel version: 5.15.21-1-MANJARO (64-bit)
KDE Plasma Version: 5.24.2
KDE Frameworks Version: 5.91.0
Qt Version: 5.15.2

ADDITIONAL INFORMATION
Also had this bug in a Ubuntu laptop, but I didn't collect details
Comment 1 Andrey 2022-03-28 12:36:04 UTC 
That's probably XKB-specific behavior as it consumes the combination on key presses immediately:
https://gitlab.freedesktop.org/xorg/xserver/-/issues/258

We could try to overrule that on Plasma side with modifier-only shortcuts but that's another story.