Ableton Forum

When you end your MIDI clip record still holding a sustain pedal and then play that clip and make it stop at it's end the final sounds will be sustained forever, until you press and release the sustain for that channel. Same thing if you use sustain somewhere between, say, 1 and 2-nd bar of your 2-bar clip and then stop the clip after 1-st bar - the last notes from 1-st bar will stay sustained. I think it can be considered as a bug, because it can make a catastrophy in a live performance. So, the decision is to make the clips send "sustain off" command every time they stop.

i think that most sequencers do that...they need an 'off' command for the sustain pedal at the end of the clip otherwise it remains 'on'.