Same issue here. Server 220.127.116.1140 and OpenPHT 1.8.0..
I hope that Plex can look into this.. They mentioned a change to metadata in the release notes.. I have a feeling that somehow OpenPHT is just seeing both your photo library and its internal fan art/background art as the same 'library'.
I hate reverting to older versions and I'm ticked at myself for upgrading when PMS 1.7 was working just fine for me..
I'm upgrading my main drive tomorrow and cloning this one.. Maybe I'll revert on the new SSD and so long as there are no ill effects, just stay on version 1.7.xxx until it can be verified that OpenPHT works as expected..
With an HTPC I feel that OpenPHT (and Plex Black Edition skin) is a must.. Awhile back I had to use Plex Media Player and hated missing my photos so much that I went back to OpenPHT even though it had errored and deleted all my preferences..
Maually re-doing all my prefrences so I could get a photo slideshow back was well worth it.. I'd do it again if I had to..
I'm mainly just worried that the regression is going to mess with shows watched since the last version...
Can you verify @paulhuntterry that your 'watched' shows didn't change when you downgraded PMS?