Error when uploading file with unicode characters in the file name

When uploading a file with unicode (utf8) characters in the file name, I get the following error.

Upload failed: The upload was canceled because there was an error in the server.
Server error is:
java.io.FileNotFoundException: ...\kunagi\files\...\?????_???.xls~...(file name, directory name, or volume label is incorrect)

This does not occur when uploading files with English file names.