It looks like it’s only registering spells cast in the last turn rather than for the whole fight, or something along those lines (the behavior seems a little inconsistent). Might be a set number of creatures or somethin’, it’s a bit hard to pin it down. Also, it will recast spells if there hasn’t been three different ones cast in that period, which might be something that could stand to be in the spell description.
Minor and incidental, maybe give it a check so it won’t cast if there’s no spells to copy? Safety check for those poor souls that might fat finger the spell on the first turn, heh.