weird Loop Playback/Groove Problem

[perfectdrug6]

This is a strange issue, but when I'm working in a loop, I program my drums with midi, using virtual instrument xpand2 and structure free. I work very long getting a groove together adjusting velocities, note lengths, quantizing, but after I get the groove I want it changes on its own, I swear. It seems any button I press basically even switching between the grabber and selector tools, zooming in and out, changes the groove. It changes what things are emphasized in the loop, like the kick won't hit the same or the snare, and makes it impossible for me to keep the groove. Trying to duplicate the loop in any way whether dup, repeat, region loop also completely changes the groove. I've experimented with H/W buffer settings to no avail. If anyone has any ideas about what this is or have experienced something like this any help would be greatly appreciated, because I'm losing what's left of my mind.

Using pro tools 8.0.3 LE, Mac G5 Dual Core 2.3 4GB Ram, Lacie External 250GB, Axiom 25.