You've never had contradictory user requirements thrown at you, with the expectation that you somehow implement them both? By this definition all software with more than one user is buggy, and it's impossible to do otherwise until we get AGI to do everything.
Unexpected behaviour is how I choose to define "bug".
It doesn't matter if the programmer intended it. It's still a bug if it behaves contrary to the user expectation.
It might be that the best resolution is better documentation / training, but it's still worth of a bug being raised to fix.