When linking files with special characters in their name (German umlauts, to be precise) on an Apple Macintosh system, exporting the project and transferring the whole stuff to a windows system, everything looks perfect, but
- links in the indd file to assets with umlauts are recorded as missing
- relinking on a per-folder-basis does not find them, either

Workaround: re-link each file on a per-file basis.

Guess there is something wrong in the way indesign handles the file names internally (i.e. some encoding issue).