Replaying to myself
I made an album with pi9ctures, same name as the post. Still not clear why I was able to directly upload pictures on Tek500 post and not here (maybe there you cannot make a picture folder; didn't check that yet)
Forgot to mention that those blue annoyances disappear when Clear Menu button is pressed (that state is presented in the last - or first - picture).
Wave-forms are from FG502, different points of triangle generator schematic - if interested about another device with abnormal behavior... there it is