Sure, the bug that lasted until the next fight was caused by the skeleton enemy, but it happened with other type too (it just almost instantly fixed itself... or maybe I got to the next fight so quickly that it made me remember it like that). Unfortunately I don't remember the second one.
I was battling a lot (I played for around 2 hours) and it happened only these two times.
Well... My brain didn't even registered how the defend option works, so... :'). I used it once out of curiosity, nothing more. Probably my character was so powerful that I didn't need it (I invested points in everything except the defence).
Battles have their charm, no doubt about it. They definitely feel chaotic, but most of the time they are understandable.