Seperate custom roles from pre-defined roles in the custom view definition window
Custom professions are split from pre-defined professions for the purposes of adding their columns to your views, but custom roles are folded in with pre-defined ones (presumably, because they came much earlier). For the purposes of parallelism it would be smart to tease them out into their own category. Minor improvement.
The difference is that a custom role and a default role are essentially the same thing. Additionally, a custom role can actually override a default role. I'll see what I can do though.
Do you save custom roles that overwrite default ones as custom roles? I thought that they were treated as the new default by Therapist, but what you're saying makes sense, since the only way to restore a default role you've overwritten in this scenario would be to mess with game_data.ini.
If you create a custom role that has the same name as a default role, it will notify you, and that custom role will be used in place of the default role. Removing or renaming your custom role reverts back to the default role.
Custom roles are saved in the Dwarf Therapist.ini, and the default roles in the game_data.ini, so there's no risk of deleting a default role (unless you edit the file).