Just another bug report =P
I don't know if this is significant but here it goes...
After doing a search for "asakura ryoko" in the character field, I bookmarked image 29866
No problems so far... then, in the same page, I try to bookmark image 26093
No problems again... or so I thought... I looked at the first image, then I see that it isn't bookmarked at all... so I check 'My Favorites' and it tells me that I haven't bookmarked any favorites at all.
I've tried it several times both in the search pages, and in the normal view, and I've also discounted the possibility that the page, "This user has not marked any images as favorites" page could be cached.