TFS2012 builds don't discover all unit tests in VS2012 solution - unit-testing

Question

Another day, another problem with VS2012 and unit tests: Our solution has three test projects, together containing 335 different unit tests. All of these tests successfully run locally on different machines, but when checked in to our TFS 2012 build server, each time only 235 tests are being discovered.
There are 15 different test classes containing the unit tests, some of them using the new Fakes framework, others MOQ, some none or both. All of the classes reside in test projects (assemblies) ending in Test, the classes themselves are all ending in Test.
Some classes are not being discovered at all during the test run as part of the build process, in other classes e.g. 8 out of 12 tests are discovered and run.
Taking the "8 out of 12" example, the [ProjectNameTest].dll that's being generated shows all 12 tests using .NET Reflector 7.0, it's just so that some of the tests aren't run. I also cannot find any similarities (e.g. tests using Fakes / MOQ / ...) among the tests not run / discovered.
The build settings being used define the Test Sources Spec as **\*.dll (it used to be **\*test*.dll, but I changed this just to make sure that all files are taken into account).
For the Run Settings I initially started of with no Run Settings File and CodeCoverageEnabled. As part of trying to solve the problems I also changed this to a user defined UnitTest.runsettings file, unfortunately with the same result.
Does anybody know why there are all these problems? What might be the reasons? VS2010 and Moles worked a lot better, VS2012 has been causing a lot of trouble recently.
Update
Months later we finally updated the TFS installation to Update 3, but this made things even worse. Unit tests on the build server don't run anymore at all. Enabling dumps and analysing them showed that a StackOverflowException is thrown, but there is no indicator about the test that might be causing it. Again, locally on different developer systems the tests run without any problems.
We are considering opening a call at Microsoft as we've spent far too much time getting the whole thing to work (again). Moles were a whole lot better... I will keep this updated as soon as there is some kind of progress.
Update 2
Another few weeks have passed, and no real solution yet. As we have moved from VS2012 to VS2013 (Premium each time) now, we discovered that all tests are now run as part of the build process (again). Unfortunately, we still have problems getting all tests to pass - locally, everything runs fine on multiple systems, on the build server about ten percent of test fail. Investigation to be continued...

Answer 1

Usually, when tests pass locally but not on the build server, you probably need to include your assembly dependencies or if your tests are using databases you are connecting to the database properly.

Answer 2

Finally an answer was found - the problems with test failing randomly on the TFS build server were caused by using the Microsoft Fakes Framwork. On our local systems, everything worked as expected - we had Fakes defined in our different unit test projects (generally one test project for each "normal" project).
On the build server all the fakes were generated in the same directory, therefore depending on the build order of the projects (which in parts may be different for each build), the fakes generated first were overwritten by the fakes from the following project etc.
Instead of having the fake definitions as part of every project in our solution, we changed it so that we have a solution wide definition of fakes (e.g. System.Web.Fakes.dll) that we link to from each test project where we need it (Add existing item => Add as link). This solved the problems with running the unit tests on the build server, all tests pass again.