Help diagnosing constraint issue in BulletXNA RagDoll Demo.

[xexuxjy]

I'm looking for help diagnosing a bug in my c#/xna port of Bullet (http://code.google.com/p/bullet-xna/) . All the demos I've done seem to work fine , apart from the ragdoll demo where
for some reason the bodies become very 'twitchy' (I've put up a video of this happening in slow motion at : http://www.youtube.com/watch?v=1hnI97l_Mdw&feature=plcp)
I've tried all sorts of things including capturing and logging all the values in both the c# and c++ versions and comparing them to get an idea how and where they diverge but haven't been able to track it down.
Does anyone familiar with the library recognise the sort of problem shown in the video and can maybe point at a particular area of code to check?

Thanks,