Why can VS 2012 build in parallel on some of my cpp files?

Question

I have a big C ++ project that I am compiling with MS VS 2012 from the IDE.

I turned Multi-processor compilation (/MP)it on and the assembly starts in parallel (I know this because 8 instances cl.exeare visible in the task manager). However, after a dozen or so files have been completed, the assembly seems to be serialized and only one instance remains cl.exe.

I checked incompatible options (as indicated here ) and everything seems to be correct. I also built using jomthe command line, and the build is much faster, and all the kernels have a much larger part of the build time.

Questions:
Is there a limitation when building in parallel in VS?
Or are there any new settings that I can skip?

Any suggestions are welcome.

EDIT

Here are some screenshots showing what is happening. When the build starts, I get a lot of compilation (see Lots of instances of c1.exe in Task Man), but after a minute or so I got to one or two instances. This doesn't seem like a compiler restriction or a problem with the project, because creating with jom is about 4-5 times faster (using the VS compiler) than creating from the VS IDE.

VS 2012 Immediately after starting assembly VS 2012 One minute after the start of assembly