Hmmm it's been like it for a few weeks and I've only just got around to posting about it. Today I checked to make sure it was doing it by editing or with a plugin, and it seems to be not doing it at all now. So I don't know... it's fixed itself.
1. What skin are you using? 2. Have you made any alterations involving viewed or viewdate? 3. Have you changed your Windows Regional Setting for date? 4. Does this happen when any kind of change is made? 5. Does it happen if the record is updated with a plugin?
Whenever I make an alteration to a movie file the date seen entry is blanked out on saving. This has probably started with the last update for me, but I may have missed it. Unfortunately it means some of my films have had their date seen wiped out.