I've run into this in several different builds now, on and off. Sometimes it is fine, and sometimes the mouse tile selection is way off.
I'll try to demonstrate with screenshots, but since the mouse cursor isn't captured, I have indicated its position with a red dot:

As you can see, small mouse movements within one tile can often result in a nearby tile being highlighted. I can get the selection to blink between tiles just by moving the mouse a few pixels in random directions. 

This doesn't always happen, but when it does it is very annoying. I seem to remember seeing this problem on tactical maps as well, but don't have a definite confirmation of that.

I will pose a guess:

As I rotate and zoom the camera, I can vary the amount of error, and the error is always greater towards the edges of the screen (nearly a full tile) and smaller in the center (just under half a tile). Perhaps it is due to a mismatch in the 3d projection of the world and the inverse projection used for the mouse position calculation? Perspective projection would account for the higher error at the edges, but possibly also the position of the viewport within the larger map makes a difference, explaining why some games are fine (spawn near the center of the world) while others are really bad (spawn near the edge).