A generic class whose formal generic parameter G is constrained by
non-expanded class FOO has a routine that takes an argument of type G
and passes it as the target in a call to an agent with an open target
of type FOO.  A second class inherits this class and provides FOO as
actual generic parameter.  The actual argument in the call to the
routine is of type `expanded FOO'.  After initial compilation where
the system is frozen, the actual generic parameter is changed to
`expanded FOO' and changes are melted.  Then the actual generic is
changed back to `FOO'.  System execution then dies with a segmentation
fault.

Discovered in release 5.4.0610.