Fairly certain it's not intended, as power armor does not actually cover the head in the encumberance/protection/description menus. There's also the fact that power armor helmets are an item in the game.
No, what I meant is that it is intended to be worn ONLY with power armor components essentially refusing to be worn if the condition is not met during the action.
UPD. Checked with an older version of Cata. Just as I thought:

However you are right about it being a bug (or a recent chance I am not aware of).
It did allow you to wear different clothing types before.
