"allowed-values" data not showing up in resource metadata

Jaikiran Pai reports:

IIRC some releases back, if an attribute in a domain model resource,
allowed a certain set of values, then a read-resource-description via
the CLI would show the allowed values. But checking against the latest
upstream, I don't see it available any more. For example the
timeout-unit attribute of the strict-max-bean-instance-pool resource no
longer shows the allowed values:

[standalone@localhost:9999 /]
/subsystem=ejb3/strict-max-bean-instance-pool=slsb-strict-max-pool:read-resource-description
{
"outcome" => "success",
"result" => {
"description" => "A bean instance pool with a strict upper limit",
"attributes" => {
"timeout-unit" =>

{ "type" => STRING, "description" => "The instance acquisition timeout unit", "expressions-allowed" => false, "nillable" => true, "default" => "MINUTES", "access-type" => "read-write", "storage" => "configuration", "restart-required" => "no-services" }

,
...

A quick look at the resource he mentioned shows that TimeUnitValidator is registered as the validator and it implements AllowedValuesValidator. The standard AttributeDefinition metadata generation logic is checking for AllowedValuesValidator and is using that to create the "allowed-values" metadata. So on the surface it looks ok; must be something subtle.