build.ninja is not closed during build

QtCreator seems to keep the file build.ninja (when using Cmake with ninja) in build directory open.

When some of CMakefiles.txt of the projects are modified, cmake is supposed to be rerun to update build.ninja when I start a rebuild in QtCreator.
However, due to file locking on Windows, cmake cannot overwrite the build.ninja kept open by QtCreator.
The problem occurs only when QtCreator has opened the project.
When I run "cmake <builddirectory>" while QtCreator is open, only the build.ninja file is not modified, while other generateds files (the .cbp etc) are all updated by cmake.
As soon as I close QtCreator, "cmake <builddirectory>" also overwrites build.ninja.
I cannot find an open handle for build.ninja. It seems to be opened only briefly.
I also notice a long freeze after the message "-- Configuring done" of cmake (before "-- Generating done").
During the freeze Windows does not allow renaming the file build.ninja.
Maybe the file watching of QtCreator and the file writing of cmake leads to some kind of deadlock.

build.ninja is opened in QStringList CMakeProject::getCXXFlagsFor(const CMakeBuildTarget &buildTarget) in src/plugins/cmakeprojectmanager/cmakeproject.cpp