Thumbnail links back to gallery page??

Gallery URL: http://www.brownsauce.org/gallery/brownsauce
Gallery version: 1.5.4
Apache version: 1.3.33-6sarge3
PHP version: 4.4.4-0.dotdeb.1
Graphics Toolkit: ImageMagick 6:6.0.6.2-2.7
Operating system: Debian (stable)
Web browser/version (if applicable):

Hello,

I've recently noticed some odd behaviour in my gallery. Certain images when clicked on will simply reload the page rather than taking the visitor to the intermediate, larger version of the image. The URL in the browser will briefly change to display the image page's URL before reverting back to the originating page. If you go to (http://www.brownsauce.org/gallery/brownsauce?page=37) and click on the last image (Lionel Richie), you should be able to duplicate this behaviour. So far I have yet to find any sort of commonality with the pictures that behave this way and those that behave normally.

I've rebuilt the thumbnails, but this had no effect. Would anyone have a suggestion of what's going on here? Is this a documented issue?

Many thanks, Brad