I created a new prefix and then went to register a new feed. When I click on the prefix drop down on the Title Template field, no prefix shows up. Im using XF 1.1.4.
Its related to custom user groups. The prefix shows up when I create a new feed that has the prefix with a useable user group set to "Registered". If I change the prefix useable user group to a custom user group, the prefix does not show up when creating a new feed.
This is a bug that's fixed for 1.1.5. As a workaround, you just need to make sure that you the admin can use the prefix (so if you're in a group for admins, just select that).