I have a very basic upload script, probably lifted straight off the php.net/move_upload_files function page.
move_uploaded_file() is failed because it canno
move_uploaded_file()
I had the same problem, where 'tmp_name' would say it is being stored in '/private/var/tmp/' but the file would not exist there.
I had to add "E" to my "variables order" in php.ini ; variables_order Default Value: "EGPCS"
Hope this helps.