I had a switch statement which tests characters, and accidentally entered case "q": instead of the required 'q'. When I tried to overwrite the double-quotes with single-quotes (with the keyboard on overwrite mode), ReSharper autocompleted the single-quotes, which resulted in a bit of a mess.

There shouldn't be autocompletion when the keyboard is in overwrite mode, at least if the carret is not at EOL/EOF - presumably when someone overwrites mode they know what they're doing...