Here's some conclusions I came to while riding Ellie this morning:
She's a crabby witch of a mare that spent 12 years as a trail horse. She's got no work ethic at all, and has been allowed to get her way FAR too much, and she's SMART!
Here's how a ride with her went the first time I rode her: great till she gets to the gate, then, she's done. When you try to steer her back out that's where the fun begins. She'll cow-kick, crowhop, wring her tail, and carry on - that is until you give her a little swat with the whip, then business as usual until you get to the gate again. It took me 5 or 6 rides to really get her going well, now she tries her tricks ONCE, and then gets right to work - and is she ever a lovely little thing. I convinced the owner to switch her from a curb into a snaffle, and she moves like a perfect little dressage horse now. honestly, if I could afford another one I'd probably buy her.
You could have spent a year with this horse trying to fix her "pain" issues (if she were mine I'd probably have her in a different bit for other reasons, but the plain snaffle is 100% better then the curb!) and gotten nowhere. All she really needed was some stiff discipline. Apparently she's still a nappy little witch with the lesson kids, so she's still for sale - but I expect she'll be bound for a better home now that we know she's a good horse as long as she gets good riding.
I still think that 90% of bad behaviour, especially out-of-character behaviour is related to something being a little "off", but in this case acting somewhat naughty is actually in character but undesirable. In Ellie's case, she had years of training that "if you scare the human you don't have to work", so this is what she does.
This is where the advice to just ride through it really comes to mind. The first time Ellie and I really had it out she was pretty determined that she was NOT going to work, and I was determined that she was - and if that meant we were going to circle the arena in a crow-hop rather then canter, then that was how it was going to be... I was in a western saddle, I'm not going anywhere! Then, the lightbulb went on that she had to be nice for me, and all is well in the universe.
You have to always keep in mind that most horses don't care about working. Sure, they can enjoy it while they are doing it, and some horses have better work ethic then others - but they'd equally enjoy sitting in the pasture all day eyeballs deep in a round bale. It's up to the human to convince that horse she's prefer to work nicely.
It's the good horseman that can look at a situation and be able to figure out why the horse is being a pill, and make the call as to weather it's a dicipline issue or a physical pain issue. It's a fine line, because there is nothing worse then beating a horse for telling you it hurts.