I’m not sure what happened, but I just upgraded from Build 20101012 to Build 20101102 of Safecracker and have run into an issue with a form that includes a safecracker file field. There is a required field in the form, and now when you submit the form with a file in the safecracker file field, it removes the file and bring up the error page that says the field is required. Any idea what could have changed in between those builds that would cause that? This is working properly when you submit an entry through the Control Panel, but not when you submit through the safecracker form.
Let me know if it would help to see the form or code.