Message-level custom parameters in tool configuration ignored

The custom parameters included at the message level in a tool configuration submitted to the registration endpoint (/mod/lti/openid-registration.php) are not being passed in the respective messages (e.g. a LtiDeepLinkingRequest or LtiResourceLinkRequest message).  This issue can be replicated by submitting a tool configuration which includes message-level custom parameters; e.g.:

            {
                "type": "LtiResourceLinkRequest",
                "custom_parameters":

{                     "launch_message": "true"                 }

            }

These parameters appear to be completely ignored.  (The test tool at https://saltire.lti.app/tool has been updated to include such parameters.)