After the third version of Visual Studio, this bug is still not resolved. Here is the simulation:

If you have a framework or a project which you have in all of your application projects, thus added as a reference to your application project
If you have the framework project opened as well as the application project opened
If you do multiple framework compilations
Every time, you will also compile the application project so it would benefit of the new updated DLL
If you do that 20 to 40 times, you will see that the application project, after a while, will show a bunch of errors because it looses reference to its reference DLL
Thus, you have to close that application project, start it, and you are good for another 20 to 40 similar patterns