Most add-on functionality, including accessing master phrases, templates, template modifications, and pretty much everything else used for development now requires development mode to be enabled.
We do need to make a change here though related to the admin navigation stuff. I suspect the admin nav stuff is displaying everything in debug mode, but then going to any of the development related items probably complains you haven't got development mode enabled.
Actually, I've never had development mode enabled before when I exporting my add-ons. Should I have this mode enabled from version XF 2.1 when creating add-ons?
Well, you'll need it now It wasn't exactly required before, but if you want to create data like templates, modifications, code events, custom BB codes (everything) then you will need development mode enabled.