I noticed the same situation on my developer machine today. I installed the ArcEngine runtime, and provided a single-user authorization code for the engine developer kit. I also noticed the name of the desktop license server under the Engine section, but I thought it dealt only with concurrent licenses and not single-use.
I spent most of a day trying to get a pagelayout control to work on a Windows form in my custom extension. The only way I was finally able to view the pagelayout in design mode was by adding a license control to my form, and adding the RuntimeManager.Bind(Engine) in the New() contructor (before InitilizeLayout is called). It seemed to display fine in design mode using .Bind(Desktop) or Bind(Engine). However, when I debugged the app, I got a mysterious error "(missing) license not available. Check for Single-use license in ArcGis Administrator". The error message did not mention which license was unavailable. By right clicking the license control in the IDE, I was able to select other license levels. I typically run ArcInfo license, but when I chose that level exclusively on the license control, the form crashes in Visual Studio 2010. So far, I can only get my extension to run properly by using an Editor license in the License control properties, and by switching the ArcGIS Admin to use an editor license from our pool.
This whole process with binding and licensing a pagelayout control in an ArcMap extension in very tedious and seems altogether unnecessary, since I am required to have a license anyway to run ArcMap. I hope someone can explain to me a better way of doing this. The other recent thread from Melita at ESRI gave me some ideas, but did not solve my problem. I'll try clearing the license server name from the engine tab of the ArcGIS Administrator and see if that works. I wonder what other surprises will occur when I go to deploy!