Right now you have two choices:
1) Listen on all interfaces (Default, with Interface = 0.0.0.0)
2) Listen on one interface (Interface = 80. ....)
My machine has three addresses, hiawatha should listen on two, and a svn server should listen on the third.
You can use two Bindings with Port = 80 and a different Interface setting, but having just one Binding with Interface = IP1, IP2, ... is a bit better IMHO
In any case, wigwam did not catch this error. If this is a bug in wigwan or in hiawatha is up to you
Hiawatha version: 6.9
Operating System: FreeBSD