When you are using lots of VST effects, reverbs, overdrives etc and VSTI, the "stop" command in pattern editor seems to keep ends of reverbs, distortions etc of last notes played, if they haven't had time to finish naturally.
The result is when you press play, then you hear those ends of notes, even if you restart the song from the beginning...
And more, if you save your song in audio format, you will also hear that sounds in the beginning of the final wav/mp3...
Could there be a real "immediate and absolute stop ALL noises" effect when you press "stop" ?
I think it's like a problem of clearing a buffer or something like that, maybe...