Issue with qmake generated makefile name in subdirectories

The top level directory generates the makefile with name "Makefile_g" but subdirectories makefiles are generated with "Makefile" in Qt5.6. Incase of Qt 4.8, both the top directory and subdirectories makefiles are generated with "Makefile_g" filename.

Using the below command in makefile to generate the makefile for top and sub directories with name Makefile_g.

Makefile_g: $(PRO_FILE_NAME)
$(QMAKEPATH)qmake -o $@ $(QMAKESPEC_SWITCH) $(QMAKESPEC) $<

Here $(PRO_FILE_NAME) is top level pro file.
QMAKEPATH incase of ubuntu is /usr/local/Qt-5.6.3/bin and $(QMAKESPEC_SWITCH) $(QMAKESPEC) are empty incase of ubuntu.

Donot see any qmake option difference between Qt 4.8 and Qt 5.6 https://doc.qt.io/qt-5/qmake-running.​html.

qmake --version
QMake version 3.0
Using Qt version 5.6.3 in /usr/local/Qt-5.6.3/lib

Attached is the minimal compilable example project to demonstrate the issue.

To build the example project:
cd TestQmake
make clean
make all

Is this a known issue in qmake generator make file code in Qt 5.6 and above(qmake/generators/makefile.cpp)?