Thanks again for replying, Hans. The problem has now been resolved, though. I still don’t know what the problem was, but I fixed it by exporting an omf with the “consolidate” option instead of the “copy all” option. When I did it was way, the handles were intact.
Frankly, I’m still suspicious that they are just clueless on the other end. The first problem I reported about here was never really a problem at all – they just didn’t know what they were doing.