Unable to make a media field required, with a "link" field as the controller

Problem/Motivation

When using a "Link" field, as the controller, I am unable to make a media reference field become required.

The control field, having the command "Is Filled", should(?) make the target field, required. Correct?

This is not happening.

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Is there a step I'm missing?
Or is this a bug with the fact there are two fields in LINK?