File Loop on Save

I’m having this really bizarre issue on one of my WordPress installations (I have other installations on the same host that seem to be working fine). It’s a bit weird to describe but I’ll try:

So let’s say I go into Appearance > Editor(Twenty Eleven theme, unedited) (This path: http://domain.com/wp-admin/theme-editor.php)

I make some adjustments to the style.css (I know you shouldn’t edit default themes, but this is just to give you an example of what’s happening).

I click on “Update File”. The file does not update, and the path changes to http://domain.com/wp-admin/theme-editor.php/ (with the / at the end)

Then, if I try to go anywhere else within WordPress (e.g. back to the home page), the page doesn’t change, but the path changes to wherever it should be going (e.g. Click on Dashboard and the path changes to http://domain.com/wp-admin/theme-editor.php/index.php) — Also, if I keep clicking on “Update File”, the path becomes: http://domain.com/wp-admin/theme-editor.php/theme-editor.php/theme-editor.php/theme-editor.php/ and so on.

I can add new posts and pages normally, and upload new images, but I don’t seem to be able to update certain settings (I can’t change “options-permalink.php”, for example, but I can update the “options-writing.php”, “options-reading.php”, “options-discussion.php”).

I tried to do a Google search for this problem, but I didn’t really know what to search for!

This problem has persisted on this domain (the domain if it helps is bloodofages.com) through WordPress installations, which I’ve tried reinstalling 3 times (twice using Fantastico and once manually).

I have disabled all my plugins but with no luck.

I think it might be an issue with the permissions on the php files, but I’ve looked at the permissions on this installation and on another installation on the same server, and they *seem* to match up.

I think that covers everything! Any advice would be gratefully accepted =)