have you checked there are no 'gestures' assigned to the tablet too? like a certain shape drawn, something like a left V shape can trigger undo for example. also check on your computer system. if you are on windows ive always had to turn off some settings for touch input, so that Windows recognises the wacom tablet as a mouse rather than thinking it is a touch screen, as that adds weird 'touch' input rings whenever you click too, which is super annyong but also makes it behave differently. Google for wacom, windows, touch inputs, mouse clicks, rings and see what you find, sorry it's a while since i had to fix that on my pc.
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