When using QB to build on multiple machines, the main build server farms out build jobs to other machines. If those machines are checking out source based on passed parameters (such as checking out from the config on the main server), there is no reason to have multiple configurations. It is very convenient to be able to use the same remote config from multiple configs on the main server.

Presently, it is not possible to use the same config in parallel, so you have to use multiple remote configs to farm the builds out to.

I can see a couple of ways of making it work - one is to "fork" the config every time it gets called, the other is to have the master build server pass a config to the remote server for it to run. The temporary config would then get a unique ID on the remote build machine. This would allow you to run multiple copies of the same config on the remote machine.