"Saddle vs Bareback"

My appy mare is a very marish mare and has a thing that when we canter with the saddle she thinks she can just be a bucking bronco and toss her head around.

But the in other words I can canter bareback with just the bridle or a halter and lead and she has none of the nonsence of bucking or tossing her head.

Is it possible she realises that the saddle means work?
Does she have more fun being bareback then the saddle?
She's a dream on the ground but a Real Mare when working her!
She is ridden in just a tomthumb and noseband bridle and a jumping saddle with a breast plate and martingale (not that it helps).

Tricks I do on her
Stand up, sit backwards, sit on her rump, go jockey, around the world, sit sideways, stand on her rump, lie down and lie backwards.

Advice please?

Sounds like you might have a saddle fitting problem... or check your pad maybe you picked up some dirt, or a sliver that is rubbing her the wrong way....

The saddle fits we have even had a fitter come I have no idea but if it was the saddle why would she toss her head?

Tossing her head could be a sign of pain aswell as bucking

Firstly, to clear things up, are you riding her in the western type tom thumb, with shanks, or the Australian type - A snaffle similar to a full cheek?

Tomthumb eggbutt snaffle I think

Ok, just wanted to clear that up as the western tom thumb causes a lot of controversy on here :]

To me, it sounds like a saddle fit issue - Many horses will hump, buck and toss their head if the saddle is hurting. Is it possible for you to get a saddle fitter and/or a chiropractor out?

This is my girls bit.

Yes I have had a chiropractor out and she said her back was fine but I have a saddle with an interchangeable gullet and she said that it was fine at narrow-medium

The problem with the changeable gullets is they don't alter the shape of the tree - The tree may be bridging or putting pressure somewhere that hasn't changed with the gullet.

Is there another saddle fitter you could try?