Various questions on Card Mirroring vs the RestAPI and PowerUps

Question

Cool that we now have card Mirroring 🙌, but would it be possible to get some information about how Card Mirroring works in the REST API and PowerUps (as they are not yet documented on https://developer.atlassian.com/cloud/trello/rest)

So far I have 5 questions on the matter:

1. How do you add a Mirror of a Card via the Rest API?
(Tried calling post to the "/cards" endpoint with idList="", pos="top", cardRole="mirror" and mirrorSourceId="") but that just resulted in a normal card... and it does not seem to be any changes to a source card when mirroring so a put-command would not be the right approach either... Is it a new EndPoint (or not support via API)?

2. Is it not a bug that the name of a mirrored card is a URL and not the real name? (and end up with that name if converted to a regular card)

3. The "get cards on Board" endpoint (/boards/{id}/cards) will default include Mirrored cards. Is there a way to exclude them (the mirrored cards)
I guess it would be endpoint '/boards/{id}/cards/{filter}' but what filter to give?

4. Is it on purpose (or a bug) that a mirrored card does not show CardButton PowerUp Buttons? 
they technically have a unique cardId behind the scenes so I can't see why they couldn't)

5. Is it not a bug that a Mirroring of a card is shown as a Create card action in the Board Activity interface (with the URL thing from #2 as name to confuse what it actually is)
...and if you look in the Actions via the REST API there is no way to see that is a mirroring (as the type id is just "createCard" and there is no mention of the the source CardId anywhere )

Jeff Kopko · Answer

thx, this is exactly what I was looking for!  Wish the docs around mirroring were better!

Rasmus Wulff Jensen · Answer

As for creating Mirror cards via rest API, the magic is to set the name = the shortUrl of the source and cardRole = "mirror"

Example

{"idList":"644d07374e0066a7b90eeddb",
"name":"https://trello.com/c/OUbmQ4Vh",
"closed":false,
"isTemplate":false,
"pos":114688,
"cardRole":"mirror"}

(Why the dedicated "mirrorSourceId" field is not the trigger is very very odd to me), but at least the above works

John Pujol · Answer

I was elated to see the new Mirror button appear in my cards today. That joy was soon snuffed out on discovering that it's major disability that to view a Mirror card, a person needs access to the board that contains the original card! Even third party apps allow this, nonsensical! Also not sure if its a bug but I noticed custom fields and possibly other things don't show in a mirrored card unless I include all the same members of the source board. 
Really hope you rethink and update this much needed feature Trello, else its not much good for our use case.