Touchscreen gestures don't inhibit touch events
While doing a touch gesture like swiping up for the screen keyboard or three-finger-pinch, applications will receive touch events when placing the fingers on the touchscreen. Those events can trigger unintended actions or change focus, which can be really distracting. For example when an input field was focused and no screen keyboard appeared, swiping up to reveal the keyboard moves focus out of the input field.
I don't think it's possible to inhibit those events for gestures like the three-finger-pinch one, since those always start with one finger being placed on the screen. It might be possible for the screen keyboard gesture, but that might have unexpected consequences.
In the long term we want to make sure that all actions happen on touch-release. For now we should ensure that all ongoing actions like DnD or selecting text are cancelled when we detect that a gesture is being done.