shadow build of qtscxml fails due to not finding scion.qrc

My shadow builds on dev are now ending in endless repetitions of

/mnt/build/eddy/Qt-dev/qtbase/bin/rcc: File does not exist '/mnt/build/eddy/Qt-dev/qtscxml/tests/auto/scion/scion.qrc'
/mnt/build/eddy/Qt-dev/qtbase/bin/qmake -o Makefile /home/eddy/work/Qt-dev/qtscxml/tests/auto/scion/scion.pro
WARNING: Failure to find: /mnt/build/eddy/Qt-dev/qtscxml/tests/auto/scion/scion.qrc

I note that qtscxml/tests/auto/scion/scion.qrc has been generated in my source tree; but it is apparently being sought in my build tree.
The problem may be as simple as that qtscxml/tests/auto/scion/scion.pro's last line needs to use a build-tree path for its write_file()'s first parameter.