What brand / model of UHD tv are you mirroring to?
This is encouraging that SOME Surface tablets < are > working.
It has been suggested that I might need to upgdate a driver for the Surface video card --- but if that was the case ... how can it put the Start screen on the tv for even one second?
That's the puzzling part in some ways.
IT DOES WORK FOR ONE SECOND and then stops.
If it absolutely HAD to have an adapter to make it work --- the Start screen would NEVER appear on the tv at all.
This morning I took a brief video and a still shot showing the Start Screen on the TV and will try to get them posted to Photobucket so I can link to them here. Don't think we can directly embed / link videos here.
Oops I'm wrong ... here is the still shot. You can see the Sony says it is mirroring the Surface and lower down on the left it says Scene select: General === that comes from the Sony and the start screen is very clear and sharp. I forgot to focus the camera
but it worked well enough I think.

Looks like I can only embed a still shot will have to make a link to the video ...
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It's not the missing Miracast certification since it works fine on my Surface Pro 2 which also uses Miracast for Mirroring.