Question: Should having the user preference “Type-ahead on List fields” set to true cause list fields to not act like a drop down? I was a bit surprised that when a user enabled that, her drop-down lists stopped working. She had to disable the setting to get them working normally again.

There's a preference that requires them to match exactly which I always suggest disabling (or rather not enabling)

she just disabled the Type-ahead on List fields (setting it back the way it was), since after setting it, she could only use type-ahead, and could not use the drop-down at all.