Well thats the answer I was looking for, I'll have to have a look on the hub side and make sure there is a nut there lol.
Another conclusion I have come to is that it may be due to the diff flanges that came with my Nismo diff.. stockers were one long and one short.. new ones that came with the diff were the same length..
Meh, 2way has been in for about 6 months now, if it pops out again anytime soon I'll start looking at it more closely.. I'm just happy I didn't snap an axle
Also I'm pretty sure I don't have subframe movement as I think I would have noticed the back end doing funny things (like when my HICAS was fubar'd.. that was quite noticable!) but it's rather stable and predictable so I don't think there's anything amiss there.