IF you abuse the change to the extrnal camera button... this is not a feature its a game engine error... it will remove ALL HUDs and panels not just a single unit...
Just to clarify to the OP (if it's something they'd use/like); they mean that entering, exiting, then quickly re-entering the external camera can disable the UI.
It's fiddly, and you have to get the timing right (not too fast, not too slow... ), but once you have the knack it's quite easy to do. Never really found much practical use for it in ships, but it's more fun in the SRV, especially on darker worlds and/or when a sun's setting - gets rids of the UI's rave-happy UI, and lets you appreciate the moody gloom.