Update Extension - hidden field does not update

I'm trying to modify the 'hidden' field with Update Extension API and I cannot get the value to change. I see the behavior when using the API in my app as well as via the 'try it out' button on the web page. Is there some other requirement to get this field to update? An example use case is the user shows up in the company directory but we want to change hidden to 'true' from 'false'. The API response returns a 200 but the field value does not change.