I followed these instructions (in the accepted answer) for setting up permissions on my /var/www/ folder.
I'm using the www-data group as it says to use. jdownes and testuer1 are both memebers of the group.
When jdownes (or any other www-data member) creates a file in /var/www they are able to edit it just fine. If another user (testuser1) in the www-data group goes to edit and save it, they are able to save but get the following error.

Here are the permissions for /var/www and the permissions on the file...

I have root access to the server and have been setting all permissions using putty not winscp. Is the issue that the owner is not www-data for new files? If so, how can I force all new files to use www-data as the owner?