If one upgrades or downgrades qt-devel, the value of QTDIR is not set
to the new location. Even if the qt.csh script is sourced, there is
a test that exits the script if QTDIR is already defined, so that the
old (and no longer correct) value remains. It is only by re-booting
that the value is correctly set. You'll have to find a better way of
dealing with this if you insist on putting the qt stuff in a non-standard
place. How about an /etc/qt.conf?