When I am playing druid, I am expecting that Travel Form will work the same way as regular mount. If something cannot be used on mount – you just kicked off.
So you click Hearthstone and you got dismounted. (if auto dismounting is ON in game settings).
If you clicked it on a fly – it’s your problem.
It does work if it is a ground mount though. Just doing firelands raid and when I am in travelform I indeed change to bear when hitting Mangle, so this looks like a flying form problem and as I said befor it shouldnt be a problem if you are grounded. I mean the game do detect if you are flying or not.
Druid travel form has more bugs now, beside mentioned by you. Flying speed is wrong, for example.
But we both know that it will be not fixed any soon because… who cares?