qmake 4.6.3 fails to build properly when the build directory contains spaces

I have a Qt project with the "subdirs" template. I have a batch file to build my project:

cd "C:\documents and Settings\mark\Desktop\Gui Trunk"
CALL "C:\Qt\qt-everywhere-opensource-src-4.6.3\bin\qtvars.bat" vsvars
nmake distclean
qmake

Under qt 4.5.3, the Makefile generated by 'qmake' looked like:

lib\$(MAKEFILE):
@$(CHK_DIR_EXISTS) lib\ $(MKDIR) lib\
cd lib\ && $(QMAKE) lib.pro -win32 -o $(MAKEFILE)

With 4.6.3, I get

lib\$(MAKEFILE):
@$(CHK_DIR_EXISTS) lib\ $(MKDIR) lib\
cd lib\ && $(QMAKE) c:\Documents and Settings\mark\Desktop\GUI trunk\lib\lib.pro -win32 -o $(MAKEFILE)

This has the path to the .pro file containing spaces, but unquoted, which qmake can't parse. As a result the build falls over horribly.

If I change my batch file to

cd "C:\docume~1\mark\Desktop\GuiTru~1"
"c:\program Files\sliksvn\bin\svn" update
CALL "C:\Qt\qt-everywhere-opensource-src-4.6.3\bin\qtvars.bat" vsvars
nmake distclean
qmake

then it seems to work. However, qmake shouldn't rely on my remembering that I have to set the cwd using 8.3 filenames rather than full filenames.