No I could not pin point the issue. Not quite sure what caused it, I think when the tube was fitted(wrong size) it had about 20-25psi in it and he has bounced the wheel up a curb or something causing a rather large shock through the wheel and maybe unfortunatly it was where the tube bulged and the tyre was even softer at that point. So basically he cracked the rim on something solid without noticing.
Thats the only explanation I could think off. I cannot think of any other valid reason why it would have done what it did.
Its now got a 26 inch tube in it pumped to around 35psi so that should stop any chance of what I said above..
I mean if now its built to the Sheldon Brown ways of doing it I cannot see any reason why the wheel would walk out of line due to a wheel building issue.. I mean after all, Sheldon is a legend of bike maintainence.