In the last period I became rather familiar with the PFSense project. I decided to migrate some of my firewalling devices to PFSense, first starting at 1.2.3-RELEASE, and finally I upgraded them to 2.0-BETA1. Doing the latter thing is possible since the locations only use the internet from the LAN, and have some minor settings applied locally. Playing around makes it much easier because of that.
Currently I am checking the GRE and GIF interfaces, I am using them to create an OSPF network, and there are some oddities in them
So perhaps I can see why the oddities are there and if needed correct them (or myself when I am misbehaving :))
You should test PFSense, it runs FreeBSD 8, and is awesome !