Project tree shows h/cpp nodes even if the 'contains' does not match desired condition

For example, when is used this qmake's project:

QT += core
QT -= gui
CONFIG += c++11 console
CONFIG -= app_bundle
TEMPLATE = app
DEFINES +=
contains(DEFINES, USE_FOO): include(foo.pri)
SOURCES += app.cpp

then the project's tree shows the foo.h(cpp) files, even the USE_FOO define is not specified in DEFINES.

and same things when the files directly has been specified:

DEFINES +=

contains(DEFINES, USE_FOO) {
    HEADERS += foo.h
    SOURCES += foo.cpp
}

PS: the sample project is attached.