I know there are circumstances where withholding taxes are required but in this case ... I dunno. I found this while searching the innanet.

http://answers.yahoo.com/question/index?qid=20060805190105AAx9AQi

IRS rules are a teensy bit complicated smile on this subject and a brief search didn't give any complete answers. When you factor in residing in the US and Canada it becomes even more complex.

A written statement from USAA would be the first step, AFAIK.