Renaming things in a piece of software with users with habits
One of the terrible things that happen for users, from time to time, is that their usual actions are suddendly made completely unusual by a change of version, because the name (nothing else) of their favourite feature has been changed. We understand that, and we do everything we can to avoid it, but the truth is that some of our naming conventions don't really make sense.
For example, a "learning path" is something only a guy with a degree in e-learning understands.