Manual feature prefix not working?

I can’t add a new feature prefix now. I can add ‘unnamed’ prefix, technically, but I cannot edit the name or code. Also if I add multiple of them and click minus button, they are all erased (which is probably fine since I assume duplicate names aren’t supposed to be possible anyway).
(Build 3116)

Double-clicking also does not work for me. Will investigate. Select a prefix and press Return to rename it.

That is interesting. If you select a class after adding the prefix, the title can be edited as usual.

Update: the code area is actually editable. Sorry for the misreporting