How are you doing the export? Are you using R6, and using the NotesDXLExporter functions?
If you're trying to roll your own, you might try that as an alternative. Also, remember Notes stores it's data internally in the Lotus Multi-Byte Character set, if you have it set up to do so. There might be a conversion problem between LMBCS and Unicode, so take a look at the settings on the machine and client you are exporting from to see how it's set.
If you are using NotesDXLExporter and Notes 6, then you might have uncovered a bug...er undocumented feature of Notes.
This was first published in April 2002