Certain Linksys (and possibly Netgear) routers will reset an IRC connection when a malformed DCC request is received. In fact, it doesn't even have to be a proper DCC request, the flaw can be triggered simply by sending the following string such that it is received by the user in some way.
DCC SEND "foo" 0 0 0
Presumably this is due to by the masquerading code that enables DCCs to work correctly behind a NAT.
Connect to a non-standard port and the masquerading code won't recognize it as an IRC connection.
p.s. i am lazy and am not sending this to linksys. someone else can if they feel inclined to do so. also i didn't find the problem; the workaround was trivial.
-- Regards, Cade Cairns