Why are stiff leg windmills hurting my low back?

I'm really confused about this exercise.  I do it with what seems a pretty limited range of motion.  Everything feels okay while I'm working out, but about 15 minutes later my low back spasms and just generally feels crummy.  I have tried to follow all the cues in the exercise, but I think something is going on when I pull out of a rep, like maybe instead of using my obliques I'm lifting back up with my low back.  However, even when I consciously try to engage the obliques I'm still getting the issue.

 

Has anyone else experienced something like this?

Upload a video and we could give you more accurate advice.

I get pain in the si joint if the glutes aren't working properly. When that happens, I focus on some of my physical therapy exercises and it gets better after a week or two.