If I'm going down (or up) through a directory in XBMC, and I'm pressing down (or up) repeatedly, it will all of a sudden go left. Then, I'll have to press right to get back to the directory and continue my navigation.
This is on a Acer Revo 3700. I've tried this with a few different remotes thinking maybe the IR codes were too similar on the remote I was using. But, the outcome was the same.