I think it's an issue with alt-tabbing and keyboard input in Windows. I see this every so often when I alt-tab. I'll also sometimes switch back and find my character is auto-running or standing in one spot and rotating as if I were holding down one of the movement keys.
Paragon City Search And Rescue
The Mentor Project
It has never happened to me, but I run in windowed mode.
That said, about 5% of the time, when I switch from one window to another, usually after zoning, one of my toons is doing thier own rendition of the Curly Shuffle. Spinning round and round, or run has auto'd. I just need to switch windows back and forth again to clear the issue.
I've noticed that though I don't have any macros set up, that sometimes when I switch windows when I come back to the CoH window certain powers have been used and are waiting to be used again after they recharge... but I haven't used the keyboard, hit anything, etc. Is there a way to avoid powers going off when I need to check something in a different window?