Sinister have 3 types of traps. His blue ability (Behold!) and black passive (Original Sinister) triggers even when he is stunned. This is a typical characteristic of traps, such as Nick Fury blue and JJ red.
However, Sinister purple don’t trigger when he is stunned. It neither destroy ap nor steal ap when the trap is match and he is stunned. This is a deviation from the typical traps characteristic.