Dataloss on NFS-clients who modify an mmap()'d area after closing the file-descriptor

Issue

When an application on an NFS-client (tested with NFSv3) executes the following steps, data written after the close() is never flushed to the server:

1. open()
2. mmap()
3. close()
4. <modify data in the mmap'ed area>
5. munmap()

Dropping the caches (via /proc/sys/vm/drop_caches) or unmounting does not result in the data being sent to the server.

The man-page for mmap() (man 2 mmap) does mention that closing the file-descriptor does not munmap() the area. Using the mmap'ed area after a close() seems valid (although it is bad practice).