QMake When does QMake find/look for prf files?

I want to allow to optionally include additional features into a build and it seemed to me, that prf were made for that.

So I followed the docs http://doc.qt.io/qt-4.8/http://doc.qt.io/qt-5/qmake-advanced-usage.html and entered "CONFIG += pullout" into the additional qmake parameters text input field in the build options of QtCreator which resulted in the following qmake call in release mode:

Code:

qmake.exe C:\Tobias\n\QtGLWebcamDemo\QtGLWebcamDemo.pro -r -spec win32-msvc2010 "CONFIG += pullout"

pullout.prf

Code:

win32:CONFIG(release, debug|release): LIBS += -L$$PWD/libs/ -lPulloutDLL
else:win32:CONFIG(debug, debug|release): LIBS += -L$$PWD/libs/ -lPulloutDLL
else:unix: LIBS += -L$$PWD/libs/ -lPulloutDLL
 
INCLUDEPATH += $$PWD/include
DEPENDPATH += $$PWD/include
 
message("Libraries: AHDDDD")
message("include path: $$INCLUDEPATH")

I placed several versions (with BBBB/CCCC instea of DDDD) into C:\Qt\5.4\msvc2010_opengl\mkspecs\win32-msvc2010 (which is QMAKESPEC), in the project folder and in a folder called features in the project folder.
When trying to build with QtCreator AHXXXX is being left out.

This made me create an empty .qmake.cache in the project folder, but that didn't help.

Though it somehow helped me for the case if I'm manually executing qmake on the commandline:

Code:

C:\Tobias\n\QtGLWebcamDemo>"C:\Qt\5.4\msvc2010_opengl\bin\qmake.exe" -makefile C
:\Tobias\n\QtGLWebcamDemo\QtGLWebcamDemo.pro -r -spec win32-msvc2010 "CONFIG +=
pullout"
Project MESSAGE: Using win32 configuration
Project MESSAGE: OpenCV path: C:/opencv
Project MESSAGE: Includes path: C:/opencv/build/include/
Project MESSAGE: Libraries: -LC:/opencv/build/x86/vc10/lib -lopencv_core2411 -lo
pencv_highgui2411 -lopencv_imgproc2411 -lopencv_calib3d2411
Project MESSAGE: Q MAKE SPEC: C:/Qt/5.4/msvc2010_opengl/mkspecs/win32-msvc2010
Project MESSAGE: Q MAKE SPEC: C:/Tobias/n/QtGLWebcamDemo
Project MESSAGE: Libraries: AHDDDD
Project MESSAGE: include path: C:/opencv/build/include/ C:/Tobias/n/QtGLWebcamDe
mo/features/include
Project MESSAGE: Using win32 configuration
Project MESSAGE: OpenCV path: C:/opencv
Project MESSAGE: Includes path: C:/opencv/build/include/
Project MESSAGE: Libraries: -LC:/opencv/build/x86/vc10/lib -lopencv_core2411 -lo
pencv_highgui2411 -lopencv_imgproc2411 -lopencv_calib3d2411
Project MESSAGE: Q MAKE SPEC: C:/Qt/5.4/msvc2010_opengl/mkspecs/win32-msvc2010
Project MESSAGE: Q MAKE SPEC: C:/Tobias/n/QtGLWebcamDemo
Project MESSAGE: Libraries: AHDDDD
Project MESSAGE: include path: C:/opencv/build/include/ C:/Tobias/n/QtGLWebcamDe
mo/features/include
Project MESSAGE: Using win32 configuration
Project MESSAGE: OpenCV path: C:/opencv
Project MESSAGE: Includes path: C:/opencv/build/include/
Project MESSAGE: Libraries: -LC:/opencv/build/x86/vc10/lib -lopencv_core2411d -l
opencv_highgui2411d -lopencv_imgproc2411d -lopencv_calib3d2411d
Project MESSAGE: Q MAKE SPEC: C:/Qt/5.4/msvc2010_opengl/mkspecs/win32-msvc2010
Project MESSAGE: Q MAKE SPEC: C:/Tobias/n/QtGLWebcamDemo
Project MESSAGE: Libraries: AHDDDD
Project MESSAGE: include path: C:/opencv/build/include/ C:/Tobias/n/QtGLWebcamDe
mo/features/include

AHDDDD is the pullout.prf in the features folder, but I would have expected it to be the pullout.prf in the project folder.
However this does not really help me since I do not know where I can find the makefiles generated from this call. They are not in the usual place.

I also tried to set the path to the .prf file with -set QMAKEFEATURES "C:\Tobias\n\QtGLWebcamDemo\"
which gave me this in both QtCreator and CLI:

Code:

C:\Tobias\n\QtGLWebcamDemo>"C:\Qt\5.4\msvc2010_opengl\bin\qmake.exe" C:\Tobias\n
\QtGLWebcamDemo\QtGLWebcamDemo.pro -set QMAKEFEATURES "C:\Tobias\n\QtGLWebcamDem
o\"
***Unknown option -set
Usage: C:\Qt\5.4\msvc2010_opengl\bin\qmake.exe [mode] [options] [files]
 
QMake has two modes, one mode for generating project files based on
some heuristics, and the other for generating makefiles. Normally you
shouldn't need to specify a mode, as makefile generation is the default
mode for qmake, but you may use this to test qmake on an existing project
 
Mode:
  -project       Put qmake into project file generation mode
                 In this mode qmake interprets files as files to
                 be built,
                 defaults to *; *; *; *.ts; *.xlf; *.qrc
                 Note: The created .pro file probably will
                 need to be edited. For example add the QT variable to
                 specify what modules are required.
  -makefile      Put qmake into makefile generation mode (default)
                 In this mode qmake interprets files as project files to
                 be processed, if skipped qmake will try to find a project
                 file in your current working directory
 
Warnings Options:
  -Wnone         Turn off all warnings; specific ones may be re-enabled by
                 later -W options
  -Wall          Turn on all warnings
  -Wparser       Turn on parser warnings
  -Wlogic        Turn on logic warnings (on by default)
  -Wdeprecated   Turn on deprecation warnings (on by default)
 
Options:
   * You can place any variable assignment in options and it will be     *
   * processed as if it was in [files]. These assignments will be parsed *
   * before [files].                                                     *
  -o file        Write output to file
  -d             Increase debug level
  -t templ       Overrides TEMPLATE as templ
  -tp prefix     Overrides TEMPLATE so that prefix is prefixed into the value
  -help          This help
  -v             Version information
  -after         All variable assignments after this will be
                 parsed after [files]
  -norecursive   Don't do a recursive search
  -recursive     Do a recursive search
  -set <prop> <value> Set persistent property
  -unset <prop>  Unset persistent property
  -query <prop>  Query persistent property. Show all if <prop> is empty.
  -cache file    Use file as cache           [makefile mode only]
  -spec spec     Use spec as QMAKESPEC       [makefile mode only]
  -nocache       Don't use a cache file      [makefile mode only]
  -nodepend      Don't generate dependencies [makefile mode only]
  -nomoc         Don't generate moc targets  [makefile mode only]
  -nopwd         Don't look for files in pwd [project mode only]

Because it did not explicitely complain about not being able to find any prf file, I also tried it with load(pullout) in my .pro file (also tried with absolute/relative path, with and without .prf, with backwards and forward slashes)
but I could never load it... It did explicitely complain about not being able to find the path...hooray

Does anyone have an idea what I am doing wrong?