Halo has suddenly decided to be naughty about longeing with the saddle on! The last two times I've longed her, she's bucked big and hard.
She's definitely still growing, though. I am wondering if the saddle may be pinching her as she grows and widens. Last weekend was the first time I put the stirrups on the saddle and let them dangle down against her sides. When I sent her out on the longe line she immediately went straight up in the air, rearing, crowhopping, bucking, kicking, and squealing. I did my best to send her forward - my logic being that if she is moving forward, it's a lot harder for her to go straight up in the air. After she quieted, she did go quietly around on the lunge line with a minimum of fuss. There were a few more half-hearted bucks when I asked her to lope, but nothing beyond that.
The saddle I'm using to train her is a Crosby close contact saddle. It's extremely lightweight - I would guess less than 20lbs. I would never ride her in it because I don't feel that it fits her well enough. She has clearance over the withers, but the tree is narrow enough that I think it would restrict her shoulders with the added weight of a rider. When I longe her, I tighten the girth enough that the saddle will not slide, but I do not tighten it to the max. I've used this saddle on her because it's expendable to me, and also very light.
Here is a video I happened to get the first time she decided to be explosive.
In the video you can see that I don't get her going quickly enough after the bucking subsides. In a sense, she's being rewarded for bucking by getting to stand still once she's through. It was hard to correct her while filming, and after I got this footage I put the camera aside and made sure to push her forward hard next time she tried the bucking. By the end of the lesson she was going well.
Because I'm worried about the saddle fit, I'm going to experiment and try a western saddle on her next time. It's bulkier, and the stirrups won't bang her in the sides as much as the english ones tend to. Also, I'm going to make it a priority to nip the bucking right away, because I don't want her doing it while I'm on her. I'm headed to the barn tonight, so there should be another progress report soon!