Quote - Thanks nimos100.
I want to know that you say.
Can you tell me more detaily?
How....?
Please.

A quick test you can make is to try to just pose the character manuel, try to move him into some "extreme" poses, but still maintain some reality to it. An idea could be to move his legs so it looks like the pose you are trying to use, doesnt have to look exactly like it, just close to it. Then you can see if you get the same problems as before, if thats the case its most likely the joint settings that are wrong, if you dont have any problems its most likely because the pose werent made for that character.

If its the joint editor then let me know and ill try to explain it to you. As it can be a little confusing, if you havent used it before :)