I discovered a interesting situation using the Garmin 430 and the Avidyne equipment. If say you have your flight plan set to KCRQ, OCN, SLI, KSMO. After take off you do the double click to select the path from OCN to SLI (note that you will be Northbound on this leg). If before reaching SLI you turn around and go back to KCRQ without touching the GPS. The GPS does not realize that you are now Southbound so demonstrates reverse sensing. The Avidyne HSI shows your offset of course correctly.
So I took off, was out over the ocean, which showed the path to my right. The HSI also showed it to my right. I turned around and went back, still over the ocean, and the GPS still showed I was to the right but the HSI showed the path was to my left. I tried this on the GPS simulator and it works the same on the simulator. You would think since the GPS knows your heading that it would detect the correct offset of the path.