Windows should not be resized when a press is going on
Moving windows around while the user is interacting with them in a position-dependent manner should not happen, because it causes UI elements to get out of the way, leading to misclicks.
As an example, typing with the keyboard looks like this:
The user positions the input device over the button to click it. On click down, the button will get focus, the keyboard will disappear, and the button will move to the bottom of the display.
On click up, the user is no longer over a button, so the button will not take its action: misclick.
A perfect solution would be to have applications be self-aware enough not to move the UI when the user is interfacing with it. A practical solution would be to make the compositor hold surfaces in place and shape when it knows a pointer is being clicked.