umount -f implementation

I just noticed that when I do the following:
- start a large write to an NFS mounted fs
- network partition the server (unplug a net cable)
- do a "umount -f <mntpoint>" on the machine

that it gets stuck trying to write dirty blocks to the server.

I had, in the past, assumed that a "umount -f" of an NFS mount would be
used to get rid of an NFS mount on an unresponsive server and that loss
of "writes in progress" would be expected to happen.

Does that sound correct? (In other words, an I seeing a bug or a 
feature?)

Thanks in advance for any info, rick
ps: I have a simple "fix" if this is a bug, but I wanted to check before
     submitting a patch.