I think I've found a bug:

You have two Excel 'books' open in one window. One sheet is protected, the
other is not. What I want to do is to paces a reference from one sheet into
another (in order to have the second sheet dynamically update). The bug
comes up if the sheet your are pasting to is locked. When you go to the
window menu to select the second (i.e. locked) sheet, the window changes,
but everything is locked out, and the option to switch back to the original
window is no longer available. Only what to exit is to crash out of
program.

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Dab

Cut off: yourhead to respond