What would happen is only in lowest gear (with the puller fully in) would it not jamb.
The pedals would lock half way around a stroke in both of the higher gears. I thought it was a broken pawl or something internal. On the web I read this link
http://www.bentrideronline.com/messageboard/showthread.php?p=314255&page=4
It made me think that two days ago I had been concerned about the amount of play (or slop) in the rear wheel so I tightened the nut on the inside of the cassette which obviously tightens up the bearings.
I loosened this off just a little (left hand thread I think) and wow the problem seems to be solved.

But No. it still jambed in the 2 higher gears and squeaked most of the time in the lowest gear. It also seemed to be dragging.
Seems like a cracked or broken ball bearing to me.
I downloaded the relevant pages 58-66 from here:
http://www.sram.com/_media/pdf/sram/dealers/SRAM-TechManual-MY10-GearHubSystems-English-RevA.pdf

This forum has good pics of the internals:
http://endless-sphere.com/forums/viewtopic.php?f=28&t=15216
And this one has photos of all the bits inside the dual drive
https://plus.google.com/photos/101486801025514137400/albums/5223098580972920721?banner=pwa