That's the oddest bug i've ever seen! Fixed!
In another thread, someone else said you could turn it back on after you had turned on InDesign's Application Frame but I haven't tried it.
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We were able to delete cache files (Mac OS X) for InDesign (without having to reinstall InDesign) to restore functionality:
Restarting InDesign (without having to restart the computer) brought InDesign back.