First off, she backs up fine from the ground, straight, quickly, no issues. I lunged her for a bit before tacking her up and she was doing great, listening to me and just generally being very responsive. I even lunged her over one of those little trail obstacle bridge thingies and she did great. So Her brain was working and she was fine. I got her tacked up and decided to try mounting from the mounting block (she used to be scared of it) and she was surprisingly fine (usually she walks off or tries to but she didn't try nearly as hard that day). Basically she was having an AMAZINGLY good day.
I had her walk around a bit. We did a few figure 8's, serpentines, all at a walk since the ground was mushy and I didn't want her getting worked up like she might have if I asked her to go faster. Then I had her go to one end of the arena and put her nose to the fence and stop for a moment. She was fine with it. Then I leaned back a smidge (more like rocked my weight back), squeezed her and gently pulled back on the reins to ask her to back up. She backed up fine for a few steps then I asked her to stop by releasing rein pressure, squeezing her forward and rocking my weight forward. Well she kept going backwards so I said "ok, we have half the arena left" and asked her to keep backing. Then she started jumping around like she does when she's about to blow up (rearing/bucking etc) so I pulled her in a circle nad took her back to where we started.
Each time I asked her to back up she would keep backing after I told her to stop. I tried to persevere and keep asking her until she actually stopped when I asked her to but she wouldn't. Each time I asked her to stop she'd keep going and then start blowing up if I asked her to keep going.
I would just push the matter but I don't want her to actually get me off (I can stay on really well and she hasn't come close to unseating me but I don't want to go there) and learn that rearing/bucking gets her where she wants to go. When I'm not riding I get the impression that she knows I'm in control (becuase she's perfect on the ground) but when I get on her back she feels like she's in control so she takes advantage and becomes "Satan Pony," as we called her at my camp. And at this point she pretty much is in control when I ride her. Any ideas?
She's fine on the ground, I've joined up with her, the saddle fits pretty well...
Edit: She's in a single jointed snaffle and she stops fine, really excellently actually, when she's going forward. >.<