Configuration not saved for user settings and theme configuration

Most of Drupal's configuration works like a charm, but when I submit changes to themes -> global settings after changing primary and secondary links (or any other setting on that page) nothing happens. It doesn't report any errors or save the settings, it just acts as if I've reloaded the page. I get the same problem when trying to change the users settings on user account -> edit.

Using Drupal 4.5, Php 4.1.2 and Apache 1.3.27.