Using multiple build agents in TFS 2010

In my TFS2010 environment, I have 2 machines as dedicated build agents. I was expecting that once these build agents were registered, if I queue a new build, TFS would wait for the first free agent and assign that agent to the build, but if I queue a build and another build is already running, the second build sits in a queued state until the first build is finished even though there is a build agent sat doing nothing.

I haven't set any tag filters or name filters or in fact anything else in the build definition which might tie the build to a particular server, so I'm not sure what's going on.

To test the fact that 开发者_运维百科both agents are working, I've assigned the CI build to one agent and the daily build to another and both then go to the different agents and build correctly so I'm at a loss...

TFS won't send another build of the same build definition to the same build controller, so if you have two build definitions, and each has a build queued, it will run both at a time.