I found a solution in an unrelated thread:
It seems that in some cases , the Randomness and Probability were both defaulted to 50 in the factory. Thus unwanted trigs and random notes !
To change this, clear any running sequence, and set both Random & Probability to 0 using their knobs, then make sure to save this on every projects (hold the Project & Save button, and click on the first step to save it on Project 1, as well as all the other steps, so that this is saved on every projects)
Just tried it, and it did the trick for me.