Whenever I try stealthing a taunt minion the taunt goes away.Is there a way to prevent this?
No there is no way to do so. this is because stealth stops the minion from being attacked or being seen. Another mechanic like this is where immunity makes a minion loose taunt. you can do this by bestial wreathing a beat with taunt and playing a minion with charge and you can still hit face. check this out http://hearthstone.gamepedia.com/Immune and this http://hearthstone.gamepedia.com/Stealth
This is by design.
For the minion to both prevent attacks to other non-taunt targets and to be unable to be targeted would be way too powerful. As such, taunt minions loose their taunt ability while they are at stealth.
In most cases, making taunt minions stealthed defeats their point and should be avoided, unless you have some other reason to keep them alive.