Why does the iPhone's iPod app sometimes forget playback position? I often listen to podcasts on my iPhone 3GS over several sessions. Occasionally the iPod app will forget the playback position, which drives me nuts because I have to remember where I was and fast forward to that point. Does anybody know what causes this? I can't seem to find any pattern to it.

I switch my iPhone off overnight and sync with iTunes every other day or so, but most of the time it's fine and I don't have the problem and the podcast shows up as part of the way through in iTunes itself. Also, I'm not playing anything else on the iPod in the meantime.
This could be a memory issue that the developer was forced to handle this way. All apps in iOS are subject to memory warnings at which point the app (developer) is to free up as much memory as it can by clearing out what the developer considered unnecessary information. 

Another point of of possible quitting is if a phone call is being received. Apps only have a split second to save what is crucial before quitting to make room for the call. Again, the developer has to decide what is truly important and what isn't to save.

The save position may not sound like a lot, but mobile devices really don't give developers a lot of room to play with and media of any type is a resource hog.