A nasty one too.
This is what I did to make it occur: Created a form with both an upload and a post field. Assigned the form a category to post to and a "post status" of published. Made a simple "post content template". Saved the form and inserted it into a page. Tested it, works fine - it creates a post with a download link to the file I uploaded.
Now comes the problem. I changed my mind about the the post field and deleted it from the form. So now, logically, it should still upload the file but not create a post. What it did was completely replace the Page with the information from the (now deleted) post template. It also renamed the Page with the name of the post. The real scary part was it did this if I was logged in as admin or not logged in at all. So it gave admin privileges to a user with no credentials at all.
I'm no expert in WordPress but this does not seem like something that should be able to occur, accident or not.
I managed to fix the form by re-adding the post field (which magically still contained the post template field info) then deleting the template info, saving the form and then re-deleting the post field.
Is there a security issue I'm missing here...a setting I overlooked?