Drive shafts rotation? Newbe

[john4d]

Late 2005 SE 1.9tdi 105 4dr Passat.
Upon rebuilding my repaired manual gearbox, to VW's workshop instructions, I find that the output shafts can only rotate in the same direction (either way).
I hope I'm wrong but I thought that I should be able to counter rotate, or at least hold stationary one of the shafts while the other can continue turning, by means of differential action, in neutral or any gear. All forward gears and reverse can be selected and rotational transmission is transferred from the input shaft.
I'm trying to avoid dismantling the box again, but if I have to.....
What am I missing?
Apart from a few grey cells!
John.

[zollaf]

of course both shafts have to be able to rotate seperately, as you have explained yourself. something in the diff must be wrong.

[john4d]

I was hoping for a guess at what might be wrong. A strip down again is on, I'll let you know what's wrong when I find it.
Thanks.
John.