I started experiencing this problem in the first map south of Beregost:
When move the mouse cursor to the edge of the game window to move the viewable area, it is slow to respond. Consequently, often I'm ending up using the map screen to reposition the viewable area within the map, and proceed that way. I mean, I can use the mouse to shift the screen about within the map. But sometimes is doesn't respond right away (usually this is vertical movement, come to think of it). So I resort to using the map screen to reposition the game window within the map. Hope this makes sense!
Sometimes when I move the mouse I see the desktop briefly appear.
I'm using a Logitech MK700/MK710 wireless keyboard & mouse combo. I reinstalled the software for it. The driver is up to date. Battery level is good.
Pentium Dual Core CPU E5700 @ 3 GHz
2.0 G RAM
ATI Radeon HD 4600
Windows 7 Premium Home 32 bit
Viewsonic VX2235wm monitor
1680x1050 native resolution
Is this a known issue for EE?