The current Blender version binds all CPUs of a system on its own authority to the Blender process, even after changed by user, and this is happening for each rendered frame repeatedly (see screenshot). This was never the case before 2.78 and I have never seen a program changing its own CPU bindings on Windows ever before.
Blender's compositor is also ignoring the threads count setting in the render panel and always attempts to take over all the power of the machine. This is probably not directly related to the first point, so that this might be worth creating a second task.
These behaviors make it difficult to use Blender in a more professional environment such as a render farm, because you have no control over what the Blender instances do anymore, if each one tries to hijack the entire system all the time. This can't be a good design in my opinion.
System: Windows 7 x64
Worked last: Blender 2.77