[mrks_hy]

Not from US, so can't comment on what it does for tax credit, but the treaty benefits should still apply.

Also, you should've mentioned that in your OP. Why would a foreign country's tax system care about another country's tax-advantaged investing account?

The tax withholding is seperate from any home countrystax obligations, if that helps to understand it. There are treaties to avoid double taxation that then allow claiming these unavoidable taxes at your tax residency. If you don't pay taxes there, usually you're out of luck.