That's interesting. Maybe there was just a temporary glitch with iPortals then; either between two sub-versions or (as I suggested in my posting of 25-Jan-13 - 2013 note - during some maintenance).
I might get back to some more organised testing soon and give a report, but I'm too busy at present).
Meanwhile, let me be quite clear as to your findings. Do the two users need the same KUID version of loco and rolling stock or just the same KUID (of potentially different versions)? Clearly any loco must match, but what happens when one or more pieces of rolling stock in the consist (or their products) do not match,. Is that piece of rolling stock just removed from the consist or is the whole consist lost?
As far as I can tell, different versions do not matter.
As for the rolling stock, if the products are not installed, or the cars them self for that matter, then the train is lost.
We where successfully send trains from many user's about in a small group. But it was a lot of work trying to match up content. Lots of asking, "Do you have this?" Even though we had list's of content used. Ive started work on a much smaller, US/Canada, group. But its just early rough drafts at the moment.