130 minute telnet timeout?

[Michael R. Wayne]

Trying to use a portmaster as a reverse console server.  If I do
   date ; telnet portmaster ; date
and connect to a port, the connection stays up for 2 hours and
10 minutes, then gets
   Connection closed by foreign host.

Given this, I suspected the portmaster.  But other people do not
see the problem.  Today, I tried a telnet from a Windows box and 
it stayed up for over 4 hours (at which point I killed it).

So, this suggests that FreeBSD 4.x is doing something.  A quick
browse through the source code for telnet does not suggest anything.
Any ideas?  There is no NAT involved.

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