Ah, you might just have discovered the first bug
I think I can reproduce this. Do you have "use vB" to yes. "use PP" to no, but then "use vB as standard" to no - effectively making PP the standard?
Of course, there should be a check against that, I'll fix that ASAP. for now, try setting "use vB as standard" to yes. You might have to restart your browser or delete the cookie [COOKIE_PREFIX]photo_popup (normally bbphoto_popup).
Edit:
Uploaded new zip-file. Just upload photo-popup.php again, that should fix it. Please tell me if it works out for you.