Closing sockets does not free them

Hi all,

I have written a simple server written in GNU Prolog opening a socket
for a client. After the job is done I close the streams and terminate
the program.

However, after terminating, the socket stays blocked for some time (like
2 minutes), I get a:

system_error(cannot_catch_throw(error(system_error('Address already in
use'),socket_bind/2)))

I am using it under a 64bit Linux. Is this normal behaviour or is there
something wrong with my code? To set up the socket I do:

	socket('AF_INET', Des),
	socket_bind(Des, 'AF_INET'(Host,Port)),
	socket_listen(Des, 1),
	socket_accept(Des, Client, StreamIn, StreamOut),

        repeat,
	read(StreamIn, Query),
	...
	write(StreamOut, Solution),
        fail.

To close the connection I do:

	close(StreamIn),
	close(StreamOut)

I also tried adding a:

	socket_close(Des)

But that did not help.

The full source is here:
http://www.cs.ru.nl/~lf/tools/treesolver/treeSolver.pl

Thanks for all hints, and cheers,
Lars