This is a weird thing:
I'm using a template made by myself in wordpress 2.3.3 and it works perfectly, but:
1. If the administrator create a new post or edit an existent one, the post is displayed perfectly with the custom template I made.
2. If an author create a new post or edit an existent one, the post is displayed but the custom template I made disappear and the default kubrick template is displayed from now on, without any reason.
3. If a contributor edit an existent post, the custom template disappears and the default template is displayed.
4. If I delete the default and classic templates from the wp-content folder, it just shows a blank page, with no template at all.