Thanks for reply Terrym.
Yes, they would play even after using Shift/Clear Ptn. It first made me think that I unknowingly recorded into Animoog which has its own recorder, but then I realized that changing synth was the same, the new synth would play this 'invisible" sequence with ITS sound.
If I changed midi channel, it started to play synth on ch.2 iSem.
I erased ALL three sequencers, (several times), just to make sure that nothing could be sequenced elsewhere.
Weird isn't it..
I will keep an eye on it, see if I can reproduce it, hopefully not:)