Deleting a file on submit doesn't work

If you check the 'delete' box on a filefield when editing a node, and then you submit it there is no deletion of the corresponding file. If you upload a file in the field to replace the existing one it does the following:

exisiting_file_uploaded_0.jpg
exisiting_file_uploaded.jpg

This seems like a fundemental issue, please let me know if you can confirm this to be a filefield module problem. Do I just need to upgrade from 5.x-2.3 to fix?
Thanks,
BeechyBoy