Apple Service Toolkit changes the default boot image

I am currently running a Mac Mini server that has images for the Apple Service Toolkit as well as a handful of other diagnostic images. One of these images is an installed snow leopard image. Normally when you netboot the server it will load the AST menu and from there you can chose which tests/images to boot. However, when I boot to any of the other images, such as the installed image of snow leopard, this will somehow become the default boot image for that machine. So when I restart the machine and netboot, holding n, it will automatically boot the snow leopard image instead of loading the menu system. I have tried this with multiple machine and multiple images with the same result. The confusing part is that this only affects the machine that the image was loaded on. You can take any other machine, plug it into the same connection, netboot it, and it will load to the menu system.

The Mac Mini server is behind a local router which was just added. Originally the server was on the universities network and this was not an issue but we added the router to have more control over the network that the server and test machine are operating under.

Any help or ideas would be appreciated.