Salem's TP

Salem doesn't keep her TP. In a fight the TP charge, but afterwards they'll always drop to 3. Is that on purpose or is it a bug? 
And maybe a stupid question, but what exactly is an Insta Win? I tried to figure it out, but I can't find a pattern. I thought, maybe if I kill the monster before "Round 1" appears on the screen, but I had Insta Wins also after that.

And maybe a stupid question, but what exactly is an Insta Win? I tried to figure it out, but I can't find a pattern. I thought, maybe if I kill the monster before "Round 1" appears on the screen, but I had Insta Wins also after that.