As it is currently set up, when you try to copy/paste PHP files back from WebDAV - you can't retrieve them because they got executed on the server instead of copied back (you just get result of the PHP file execution instead of PHP file itself). In order for this to work for PHP files - this is change is needed in .htaccess:
When people are using WebDAV (e.g. a mapped network drive), you can bet that none of them wants the PHP files to be executed but to act as a normal file. This means that this change should be standard option in WebDAV configuration, not special case where one has to contact support for change.