Khall, I'm so glad to hear your crew seems to have recovered well! I know what you mean about the feeling of getting lighter for more self carriage in the canter, I've felt that as well with my horse. The lighter I can get in the contact, the better she carries herself.
Imperini, I have struggled with very similar issues - my mare likes to get behind the leg, and i also lean back too much (after always being too forward!) and draw my leg up when I'm not getting the response I want.
We've largely solved this by getting really disciplined about go is GO, and she is responsible for keeping the gait without me. This meant (and occasionally still means!) more direct confrontation than I am generally comfortable with - she really liked putting around ignoring my leg, it was a lot less work, and she definitely objected to the new world order. But I was spending too much of the ride coaxing her forward, letting her "warm up", and the next thing I know it's been 30 minutes! So we had to change the pattern, and have rides where she was forward from the walk on, and I tried to notice every time my position was being compromised and then made that her problem instead of mine.
I need to remind her every ride, but the reminders are less dramatic and happen from the first time I pick up the rein. Now I can just sit with a draped leg and she motors along, for the most part.
I guess what I'm saying is, you have to take the "lean back, bring the leg up" option away. You have to notice when you want to do it, realize why you want to do it (she's not reacting) and back up the correct leg aid with whip or spur instead. Or at least, that's what worked for us!
Went back to basics today, and had a breakthrough where I realized that while I understand that the outside rein should touch the neck, and the inside rein shouldn't, too often the way I was getting that was by moving *my* hands in relation to her neck, instead of (duh) keeping my hands where they were and channeling her body (and ultimately her neck) where it should be in relation to the reins. So absurdly basic, ride the back of the horse to the front, inside leg to outside hand, etc. But I clearly hadn't fully understood what that mean before, or how to really get it! I love moments like that, and I'm excited about where this will take us.
[yeah yeah, I'm sure it's meant to be 'offered'!]
I have been trying to get her to offer this posture two or three times a ride, because i like how she is still uphill but you can actually see the back muscles " fill in" as it were, and be more engaged. 
In turn I think Pal is noticing I don't feel entirely secure all the time and is using the opportunity to expend less energy. I figure at some point though my body will get with the program and then maybe Pal too.
