The value of number sliders (e.g. the "end frame" button) wrap around to
their pre-click value when dragging them for a very long distance (e.g.
by lifting the mouse off the desk and placing it back on to keep
dragging in the same direction).
The problem is X11-specific, and due to XTranslateCoordinates using a
signed int16 behind the curtains, while its signature and the rest of
Blender uses int32. The solution is to only use XTranslateCoordinates on
(0, 0) to get the delta between the screen and client reference systems,
and applying the delta in a second step.
Differential Revision: https://developer.blender.org/D15507
a5c2d0018c