[Trexmaster]

It's possible to take the same spell you've already taken from a target, even after you're already taken that spell.

I.E. X steals Quickness from Y.

X can still steal Quickness from Y in future attempts, even if there's still other spell left to take.

I distinctly recall Spell Snatch failing (with no message) if you attempted it on a target with no spells left, and you were unable to steal the same spell before, so...this seems like a bug to me.