Image Gallery Problem

Hey guys!

I've got a really annoying problem with an image gallery I've had developed for a site I'm currently working on, the guy who coded the JS is struggling to work it out so I thought I'd ask here in the meantime.

http://richardkarlgregg.com/wellplastic/

Basically visit the link above and click 'work' from the menu, when page loads the first image seems to fade in twice (kind of flashes in twice) instead of just fading up once.

This seems to only happen in Firefox and Chrome, IE and Safari seem to be fine etc.

So I'm not sure if it's something to do with the JS that brings in each page dynamically, as loading http://richardkarlgregg.com/wellplastic/#work or http://richardkarlgregg.com/wellplastic/work/ everything seems to work ok.

If anyone has any ideas please let me know

I didn't design the site so I'm not looking for any crits on that and I'm aware of a few CSS issues etc / the web font I've used needs sorting out.

Thanks!