Multiple projects in CruiseControl.NET in the same queue running at the same time

Question

I have multiple projects within CruiseControl.NET (version 1.4.4) that I have assigned to a single Queue...

   <project name="Build - A" queue="Q1">
   ...
   </project>
   <project name="Build - B" queue="Q1">
   ...
   </project>
   <project name="Build - C" queue="Q1">
   ...
   </project>
   <project name="Build - D" queue="Q1">
   ...
   </project>

All the projects are non-triggered projects - I (along with every other developer in the division) use CCTray to manually kick off each project. The problem is: If, while project A is running, another user uses Force Build to start another project, it runs concurrently with project A. Even though they are in the same queue. I would have thought that requests within the same queue would be... I don't know, queued and not executed at the same time. I am using the default queue implementation of "UseFirst".

Any idea how to make the projects within the queue behave a little more queue-like? I'd like to add the projects to a timed scheduler, but without any confidence that the projects will not all try to run concurrently and kill my woefully underpowered build machine, I dare not try it.