Mine did this too, even on 2.10 also. It did seem to depend on how the disc was stopped. If you use STOP on the remote, it seemed to work, however if I used the PS button to quit playback, it would start from the beginning. I haven't paid enough attention to it to figure out if it is consistent though.
2.20 installed and running fine as of last night. I have read reports that some of the 40G models are getting bricked due to this update.