This has been a thing since... basically forever, I think. I included it in one of my posts about "better mouse tracking", but I figured I might as well give it a post of its own.

If you double-click and hold, in certain situations, none of the mouse procs (neither MouseMove nor MouseDrag) are called as the mouse moves. This makes mouse position tracking completely impossible in that situation, and it actually comes up quite often in mouse-heavy games.

Here's a demo: http://files.byondhome.com/Kaiochao/bug/ DblClickMoveFail_src.zip

In this demo, double-left-click on some turf (without moving the mouse at all), hold the button down after the second click, and move the mouse. You shouldn't see any mouse proc messages appear.

For some reason, in this demo, if you're not moving during the double-click, then the issue doesn't happen. However, in other projects, it can happen regardless of viewpoint motion. I can't tell what exactly causes it in those cases, though, but the fact that it happens at all seems pretty problematic. Imagine playing a shooter, running around and clicking erratically, firing full-auto or charging an attack, and suddenly your mouse stops moving unless you let go of the mouse button. It's analogous to macros sticking and not responding unless you tap them again.