Unlocked Trait slots become "Locked" while in a queue or adventure zone which lowers the player’s level.
This includes when teamed with someone at a lower level in an instance.
Wouldn't they technically not be available, if your level drops below a certain point, when matching another player, or are auto-reduced via certain zones?
I mean I don't know about anyone esle, but at say level 30, we don't have every single trait available, at least not that I am aware of!!!
But hey, more power to you Cryptic, if you want us to be fully tricked out trait wise @ any level reduction!