spaces in paths cause build failure

in my cross platform .pro file i have a path with this in it:
{{DIR_ID3_TAGS = $${DIR_EXTERNAL}"MP3 Tags"/}}
then that is used later like this:
{{DIR_ID3 = $${DIR_ID3_TAGS}id3lib-3.8.3/
DIR_ID3 = $${DIR_ID3_TAGS}id3lib-3.8.3/
DIR_ID3_SRC = $${DIR_ID3}src/
DIR_ID3_STABLE = $${DIR_ID3}prj/stable/
DIR_ID3_INCLUDE = $${DIR_ID3}include/
DIR_ID3_INCLUDE_ID3 = $${DIR_ID3_INCLUDE}id3/

INCLUDEPATH += $${DIR_ID3_SRC}
INCLUDEPATH += $${DIR_ID3_STABLE}
INCLUDEPATH += $${DIR_ID3_INCLUDE}
INCLUDEPATH += $${DIR_ID3_INCLUDE_ID3}

SOURCES += \
$${DIR_ID3_SRC}c_wrapper.cpp \
$${DIR_ID3_SRC}field_binary.cpp \
etc...

HEADERS += \
$${DIR_ID3_SRC}field_def.h \
$${DIR_ID3_SRC}field_impl.h \
$${DIR_ID3_STABLE}config.h \
$${DIR_ID3_INCLUDE}id3.h \
$${DIR_ID3_INCLUDE_ID3}field.h \
$${DIR_ID3_INCLUDE_ID3}globals.h \
etc...
}}
This all works fine when compiling on mac.
on windows, however, those cpp files just never get compiled. no error is given.

when linking, however, the linker says that those obj files aren't found (obviously because those files never got compiled).

walks, talks, acts, & smells like a bug, right?

it should either fail with an error saying "no spaces in paths, goofball!". or, and i prefer this, it should "just work", like it does on the mac