Young pony opening mouth.

[littlen]

Is mouth opening/playing with the tongue common in young ponies? If so how do I encourage her to stop!

Shes been backed a few months and is rising 5. We are just hacking at the moment.

She was started in a training bit by the previous owners. I switched her to a loose ring French link snaffle and then to a Mullen mouth incase she would prefer stability but the problem persisted.
Eventually settled on a thinner curved fixed ring snaffle with losenge which she seems to accept and is happy to have it put in and taken out. She opens her mouth wide when ridden and chews on it, mainly when I'm asking her for something she does not want to do!

She is very responsive to the aids and steering is good. She has flung her head up in protest at things she does not like but that's it.
Trainer has checked the fit of the bit and it is fine.
We have tried a caveson and no noseband but I don't want to strap her mouth shut.
I've had her back and saddle checked this week- no problems with either.
She has also recently had her teeth checked with no problems found.

I am a reasonably quiet rider and instructor does not think it's my hands or anything like that. She did it with the professional who backed her also.

She is not working as forwards as I would like yet, is it likely that in time as she matures she will grow out of this or should I nip it in the bud? If so how?
It really does look ugly so I would like it to stop if possible.

 

[SEL]

I spoke to the Bit Bank when my youngster was struggling. They advised the NS turtle top - but you can have the bit on loan to see whether it suits. 2 years down the line and she's fine in it.

Now if she messes around with her mouth its because she's struggling with something I've asked her to do, so its more of a training issue than a bit issue. For instance a leg yield on her stiffer side will often have her opening her mouth and making faces. Its my sign to go back a step and work out what's wrong!