I downgraded by installing three packages:
dpkg -i \ libqt4-opengl_4.7.1-0ubuntu9_amd64.deb \ libqtcore4_4.7.1-0ubuntu9_amd64.deb \ libqtgui4_4.7.1-0ubuntu9_amd64.deb
that can be found in the pool/main/q/qt4-x11/ subdirectory of the mirrors.
I downgraded by installing three packages:
dpkg -i \ opengl_ 4.7.1-0ubuntu9_ amd64.deb \ 4.7.1-0ubuntu9_ amd64.deb \ 4.7.1-0ubuntu9_ amd64.deb
libqt4-
libqtcore4_
libqtgui4_
that can be found in the pool/main/ q/qt4-x11/ subdirectory of the mirrors.