qmake treats absolute path as relative path

Say the build environment in Windows is setup as follows

set BASE=E:\dev

and then in the .pro file we use

 RC_INCLUDEPATH += $(BASE)/some/path

then qmake will expand this to

$(ProjectDir)\\E:\dev\some\path

It seems qmake thinks $(BASE)/some/path is a relative path due to the variable $(BASE) which does not seem to be expanded early enough.

Relevant code: VcprojGenerator::initResourceTool(), see

https://code.woboq.org/qt5/qtbase/qmake/generators/win32/msvc_vcproj.cpp.html#1135