Now, about 5% of the time, when I switch to a file, the cursor correctly appears as a vintage-mode underscore, but incorrectly behaves as insert mode. If I escape out of insert mode then everything is back to normal. I can't figure out how to consistently reproduce the effect.
One abnormal aspect of my setup (which isn't helping me reproduce the bug, as far as I can tell) is that I have cmd+s bound to "save_and_exit_insert_mode", defined as:
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