> What it may be? A connection lose?

that'd be my first guess. it is, unfortunately, not uncommon for
routers which do NAT (and some corporate firewalls) to close
idle connections on you. i used to have a cron script that
ran on the NATed system, cpu'd in, did the postroot, and then
hung around running "date" every once in a while, which was
sufficient to keep the connection open. i've lost that script, but
it shouldn't be hard to reproduce.

anth