If you have no binds to said mouse button or have binds out of the game no matter how it's setup (as long considered mouse button os wise) it will move any GUI's around.
For example for a test my middle mouse button I had bound to enter / leave vehicle. Anytime I hold that button down on a gui if one was up it starts dragging it off the screen.
a more practical issue outside the game that is driving me insane is for example my Mouse Button 4 is used to talk on Discord. Sadly this makes it very very hard to play the game because everytime I'm in a UI, etc I'm unable to do anything and have to stop just to talk because it messes it all up.
I assume should only be left click moving the UI around.
Old bug and maybe never reported but I guess I should do my civic duty
