A system has one cluster, initially with only the root class in it.
Each class the compiler says is missing (via a VD23 error or a VTCT
error) is copied into the cluster's directory.  The result is a set of
classes which, when compiled from scratch, cause the compiler to
report a VEEN error on `default' in feature `is_hashable' in class HASHABLE.

Discovered in Release 3.2.1.