I've purchased this a few days ago and have had the following bugs.
Randomly unable to do an undo until I draw more.
Randomly forgets that finger touch is off and will affect things in various ways. Such as making a line from the finger to the pencil tip.
Randomly forgetting force pressure is on and putting a giant blob down, then being normal
Randomly zooming in and out, and rotating with fingers not responding, or not responding to only one of those, until I draw some.
Bringing back the side icons when my hand touches the screen, but having not pressed the button to actually bring it out.
Randomly the brush will just act like the colour picker and will return to normal after I pick the pencil back up, but with whatever colour I was last touching.