Hi Stefan,
So far I cannot duplicate this behavior. I left my dac connected, and turned off for an hour once, and about 1 hr 15 minutes a second time.
On the other hand, some of the things I can repeat every time, other people do not have at all, so perhaps this is not so unique.
I will try again this weekend. It is an easy test, basically I just have to turn the dac off and leave the Pi on.
Pete