Steps to reproduce the issue

When you use the template overrides in Core Joomla following the process below.

Back End> Extensions > Template Manager > Select Templates Link > Select Your Template > Create Overrides Tab > Select Anything to override.

This will create an override for the specific module/component

You can modify this within the backend of Joomla, but you cannot create a second template override. Even after renaming the initial override from default.php.

Expected result

Should allow more than one template override for a module or component

Actual result

Will only allow you to add 1 template override, then when you try again, you get an error message saying "Template override exists"

System information (as much as possible)

Additional comments

Discovered at JDUK14, briefly discussed with @wilsonge