Problem with AHAH form and auto_nodetitle module

Cool module, but unfortunately I face a strange difficulty after adapting the todo example to my needs:
So far, my module works, I got even rid of the 'warning: array_merge_recursive(): recursion detected in...'-message described in another post (I think, by deleting the weight column in the form). But now I'm stuck in the middle of a strange problem: When I create a node of the new content type of the module and enable auto_nodetitle for it, all these nodes get the title "ant"! I reinstalled, emptied caches, disabled javascript, searched everywhere on the drupal site, but I couldn't find the reason for this. With every other content type, auto_nodetitle works fine.
Do you have an idea what I'm doing wrong? I didn't changed a lot of the todo module. Basically, I added a new text field, renamed the original one, deleted the weight field and changed some lines to make sure that every user can only create one node of this type (because it's part of a userprofile realized with the help of the nodefamily and the usernode modules).
You can find my module attached as a text file, I would be really, really grateful for any hint! Thanks a lot.