I’ve just heard from someone about this withholding tax issue. Mentioning no names, her publisher, based in the States, has apparently withheld 80% of her latest royalty, instead of 30%. I can’t say whether there’s anything else affecting this particular case, but if not, that’s totally incorrect.
If there’s anyone else experiencing this kind of thing, I’d recommend you make lots of noise about it to the publisher. If you get no joy, go straight to the top – they usually don’t like bad publicity, and you may get better results that way.