That may explain the odd behaviour you noticed with your up and downhill tracks. I looked at a recent garmin track of mine and it clearly showed me riding on the correct side of the road going up and downhill. Just curious if you can point to a track you've uploaded from the Holux device. I had a quick look at their web site and they don't mention whose GPS chip they are using. It's possible it's just not as accurate as the chips used by Garmin.