I have never had this problem (in Beijing or in Kashgar), though my experiences have been limited in this regard. My problems with money exchange (TC and sometimes Cash) usually arise from the changes in my signature (it's pretty intricate) and so is never 100% the same. After arguing for a few minutes and demanding a sheet of paper and stating "give me a pen I'll write my name a 100 times to prove it" they usually back down. For some reason, the numerous forms of ID, bank cards and atm cards with your photo and signature don't seem to cut it.