15.20.2 includes the following check on instances of the type comparison operator:

"The RelationalExpression must be checked cast compatible with the ReferenceType (§5.5), or a compile-time error occurs."

The "checked cast compatible" definition has been removed from 5.5.

SOLUTION:

1. Either add the definition back into 5.5; or
2. Change the rule from using "checked cast compatible" to "testing conversion"