iPhoto wrong thumbnails in Slideshow

So I was just messing around with the slideshow in iPhoto after finally transferring all my photos from my PC. What I have noticed is that periodically iPhoto gets the wrong thumbnail for the picture in the slideshow. Particularly portrait ratio pictures. It also gets worse if I shrink the thumbnail preview at the top of the slideshow. The thumbnails seem to be random photos in iPhoto, but when i click on the thumbnail that's wrong the correct picture actually appears. Everything else seems to work ok. The thumbnails are correct in the Events.

Whats up? Is this a bug in iPhoto? Is the database corrupt already after I only just imported all the photos. Interestingly I notice it even does it with some recent photos imported from my camera (not from PC).

Mark

 

Thanks for the reply.

Is there a way to force iPhoto to re-generate the thumbnails. Also, doesn't the slideshow use the same thumbnails as the ones used in the Event library? My Event library is working fine.