This happens to me ALL THE TIME
Glad to know I am not the only one (almost every time I talk to MR about this they express bafflement that such a thing could occur).
I go to the UK at least once a month (in fact I am in a UK Marriott now for 4th time in 7 weeks), so I guess I've had about 8-10 international stays (all UK) so far this year. Every single time, no points post and I have to fax the bill to Utah. Last week I got fed up and called them, and after speaking to four people and being on the phone for about 50 minutes (no joke), they were finally able to correct for me over the phone (but only after faxing directly the the very nice CSR).
This drives me crazy and it's an example of extremely poor service (or IT infrastructure) on the part of Marriott. It's ridiculous that I have to be constantly be checking the Marriott website and chasing points.
Come on Marriott, get your act together!