Yes, it can be a bit random.... I actually find the ipod behaves worse than using an SD card, although the SD card can also be funny - it uses the gracenote database (which is on the SSD) to pick it up. Sometimes it works, sometimes it doesn't (usually when you've added a new album - it can take a couple of restarts of the car before it caches it or something).
The whole thing is very frustrating, but that's OEM car audio for you.