My tester has had this problem a couple of times now:

# Executing GIT command: /media/revo/boost/test/build/boost_root> git submodule "update" "--init"
error: Your local changes to the following files would be overwritten by checkout:
        build/vcxproj.exe
Please commit your changes or stash them before you can switch branches.
Aborting
Unable to checkout 'db03e8001e0c5324adc56873eded25174f0c54d7' in submodule path 'libs/qvm'

ben@yyls03:/media/revo/boost/test/build/boost_root/libs/qvm$ git status
HEAD detached at 65dc979
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

        modified:   build/vcxproj.exe



This is when checking out the develop branch, I think.

I don't know how that file gets modified, but it's not me, I'm running on Ubuntu and only use this checkout for the tests.