ClassCastException in top-down visit

[jurgenvinju]

Describe the bug

rascal>toDefaultRec({-276798823r185339102,-173549339r466608811,0})
java.lang.ClassCastException: class io.usethesource.vallang.impl.persistent.List cannot be cast to class io.usethesource.vallang.ISet (io.usethesource.vallang.impl.persistent.List and io.usethesource.vallang.ISet are in unnamed module of loader 'app')
(internal error)
        at $shell$(|main://$shell$|)

java.lang.ClassCastException: class io.usethesource.vallang.impl.persistent.List cannot be cast to class io.usethesource.vallang.ISet (io.usethesource.vallang.impl.persistent.List and io.usethesource.vallang.ISet are in unnamed module of loader 'app')
        at org.rascalmpl.interpreter.TraversalEvaluator.traverseSetOnce(TraversalEvaluator.java:475)
        at org.rascalmpl.interpreter.TraversalEvaluator.traverseOnce(TraversalEvaluator.java:169)

This is triggered with a function like this:

value rewrite(value x) = top-down visit(x) {
   case value z => r(z);
}

value r(set[value] s)= [*s];
default r(value a) = a;