Streamed WCF-Service: Who closes the stream?

Hi all!

I'm currently developing a file upload and download server using WCF using
the streamed transfer mode.

When i download a file i open a FileStream on the server side and pass it to
the client. The client reads the data out of the stream and closes the
stream.

The problem is that the serverside file still stays locked after the
operation finished (consecutive tries to delete the file fail with a "...
File is locked by another process .." - exception). Does the server side has
to perform an extra close on the FileStream after the client has received
all
of the data?

Any hints would be greatly appreciated on this problem!

Greetings

Markus