It doesn't work for me (probably for years), but I know a workaround.
When in Preferences> Keyboard Shortcuts I can see Ctrl+Shift+! then I close Sigil, manually edit the sigil.ini file, find such a wrong entry and correct it on Ctrl+Shift+1, save the sigil.ini file and it's OK.
IMHO is not strictly a Sigil error, but a Qt error.
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