A correct system compiles fine.  Then the generic constraint in an
inherited class is changed.  The compiler correctly detects the VTGG
violation.  But when the generic constraint is changed back to its
original form, the compiler reports a VD27 violation, even though the
Parent part in the inheriting class is now valid.

Discovered in Prerelease 93.05.17.
Fixed in Prerelease 93.07.15.