Qt Creator doesn't parse DEFINES in custom configuration when using qmake -config

I have a project that has multiple configurations. e.g.

SOURCES = a.cpp b.cpp
conf1 {
DEFINES += ABC
}
conf2 {
DEFINES += DEF
}

If I add CONFIG += conf1 inside the pro file, or even as an argument to qmake in the Project section of Qt Creator, the defines are parsed correctly. However, if I use -config conf1 in qmake arguments, they're not. On the contrary, if I add SOURCES += c.cpp to conf1, Qt Creator DOES add c.cpp to the sources tree view (when specified using -config argument)