Compiling a system where A inherits an effective feature from B and
undefines and redefines it works fine.  If the feature in B is changed
to a deferred feature and es3 is rerun, the violation of VDUS3
(Undefine Subclause rule) is not detected.

Still not fixed in Prerelease 93.02.17.
Fixed in Prerelease 93.04.21.