I'm using WebKit-SVN-r30574 with Safari Version 3.0.4 (5523.15) on 10.5.2. Clicking on that link downloads a corrupted file, senuti_0.50.2b3.dmg.bz2, that won't expand properly. The same link clicked on in Firefox downloads and can be properly expanded into a good dmg.
mrowe@daisy:~$ curl -s -i http://senuti.googlecode.com/files/senuti_0.50.2b3.dmg | head
HTTP/1.1 200 OK
Content-Disposition: attachment; filename="senuti_0.50.2b3.dmg"
Expires: Thu, 06 Mar 2008 00:00:00 GMT
Date: Thu, 28 Feb 2008 08:41:47 GMT
The server is claiming the MIME type is application/x-bzip2, which results in a .bz2 being appended to the filename. This behaviour is almost certainly outside of WebKit, either in the CFNetwork HTTP stack or in the Safari application itself.
Closing as INVALID per our policy for handling bugs that are in components of Mac OS X outside of WebKit. The bug report will be tracked inside Apple via the Radar mentioned above.