Logitech MX510 Mouse sensitivity inconsistency

(Relatively) new build, haven't had problems with the mouse before. I have the Logitech MouseWare 9.80 software installed (specific to the MX510) and as odd as this sounds, the sensitivity is inconsistent. My mousepad is black, microfiber-type texture and I haven't had any problems with it before. If I open up MouseWare and then press OK the sensitivity returns to normal, but after that, usually after opening or closing (it seems kind of random) windows, the sensitivity will decrease (I think it is actually turning off acceleration). Logitech's support site is too broad to be of much use, so any help is appreciated, either suggestions or solutions. Thanks.

I'm on XP Pro SP2 (I was using XP Pro SP2 on an older computer with this same mouse and mousepad, no problems).

 

I find the same thing... especially with the fast-scroll buttons on my MX510 - sometimes they jump pages properly, sometimes they go REALLY slow.

Just thinking about it now, I wonder if it's related to some other USB device I have plugged in.. then again, I have the mouse plugged in to a KVM with a USB-PS/2 adapter, so that's probably not it in my case. I have tested other pointing devices as well (assorted other mice, a Gyro mouse, my ATI RemoteWonder) and it's possible a residual driver is causing an issue...