Qt Webkit "make install" with -prefix is broken

After building Qt5 from src package the "make install" does nothing for Webkit.

1) created src package from #dev (syncqt ran for the source package)
with qtsdk.git/release-tools/mksrc.sh
2) top level configure:

configure -opensource -confirm-license -debug-and-release -release -nomake tests -nomake examples -qt-zlib -qt-libjpeg -qt-libpng -angle -plugin-sql-psql -plugin-sql-sqlite -plugin-sql-odbc -openssl -prefix c:\work\build\PADDING

3) top level in source build with "jom"

4) for each submodule we run "jom -j1 install INSTALL_ROOT=<path>

For webkit this is:

jom -j1 install INSTALL_ROOT=\work\build\qt5_workdir\qt5_install_root\submodule_install_essentials
(Execution path: c:\work\build\qt5_workdir\w\s\qtwebkit)

All the other submodules export their content correctly (as with non prefix build) except qtwebkit.

If we configure without "-prefix" this problem does not occur.