.gif extension being added to .jpg files.

Gallery version (not just "2"): 2.0.6
PHP version (e.g. 4.3.11): 5.1.4
PHPInfo Link (see FAQ):
Webserver (e.g. Apache 1.3.33): lighttpd/1.4.13
Database (e.g. MySql 4.0.11): mysql 5.0.18
Activated toolkits (e.g. NetPbm, GD):
Operating system (e.g. Linux): Linux
Browser (e.g. Firefox 1.0): Any

Site: http://www.edgegrove-school.co.uk/index.php?option=com_gallery2&Itemid=287

The old site worked fine which was on an Apache server. I've copied over all of the settings but you'll see if you try to save one of the blank thumbnails, the system has appended a '.gif' to the filenames. Any ideas? Maybe it's a GD/Netpbm issue but I've not had any problems with other sites on the server which use other systems that utilise both gd and netpbm. If you click on one of the blank thumbnails, it works though.

Thanks, Richard