Shift-Alt-B and I are regarded as ambiguous shortcuts on Mac with standard UK or US keyboard layouts

To reproduce, build and run the attached test app, which registers two menu entries with shortcuts Shift+Alt+B and I (i.e. capital letter 'i').

Type Shift+Alt+B and observe in the application output that this shortcut is ambiguous.

On the face of it, this feels similar to QTBUG-117365 and QTBUG-115040. However, in ths present case, the character that Shift+Alt+B produces is actually a letter, rather a dead key or a symbol. It's this that seems to be causing the problem here, as Qt then tries to convert it to a capital letter seeing that shift is held down. See also QTBUG-58086 which was a problem with the same shortcut and the key sequence widget.