I've noticed that Limewire (and possibly other servlets, although I haven't noticed it with any others yet) do not properly detect their IP address when behind a NAT. In the case of a push-proxy this might not be an issue--however I have noticed it in several cases where the firewall is forwarding the correct ports (thus doing away with the need for a push request)

Aquisition has not thus far displayed this behaviour, although I have not had the chance to check the same quantity of hosts.

I don't know if there is anything any of you developers can do to have the host detect the correct IP, and the number of hosts behind a NAT which are not push-proxied are negligable, but it would still be worth solving if you have a few extra minutes.