I can't really think of anywhere else this would be coming from, but the referrer in the watchdog suggests it is done on the field changing.
Basically, I get this error
The directory sites/all/modules/jquery_ui/jquery.ui/themes/default is not writable, because it does not have the correct permissions set.
from referrer:
http://dev.local/admin/content/node-type/project/fields
I'm not sure why this is required exactly, but some notes about it should be included if it is.
Comments
Comment #1
gnindl commentedUse the function file_check_location instead of file_check_directory for checking the existence of jquery_ui theme subfolder. file_check_location doesn't require the directory to be writable.
Patch committed to the repository.