"curl" makes form submission result in 404

[eluser]Bramme[/eluser]
Okay, after some delays, I finally got to working on the problem. Sadly, nothing worked. I commented out the send_notice thingies, deleted the validation rule for the field, changed the form action to $this->uri->uri_string(), nothing is working. When there's lots of text, I get a 404, when there's little text everything is okay.

And to answer manilodisan's question: no, the global xss filter isn't enabled. Anyone else got a clue?


edit: Okay, I'm fairly sure it's got something to do with validation, because when I enter only the long text in the area and leave all my other forms empty, I get the 404 too. Else validation always succeeds.