Mentions are broken in adaptive cards when responding to Universal Actions

I have a problem using mentions in responses to universal actions. Say my bot sends a message with an adaptive card to a Teams Channel:

{
  "type": "message",
  "attachmentLayout": "list",
  "attachments": [
    {
      "contentType": "application/vnd.microsoft.card.adaptive",
      "contentUrl": "",
      "content": {
        "type": "AdaptiveCard",
        "version": "1.6",
        "body": [
          {
            "type": "TextBlock",
            "text": "<at>Lars Knoll</at> created the incident"
          },
          {
            "type": "ActionSet",
            "actions": [
              {
                "type": "Action.Execute",
                "title": "Submit",
                "verb": "submit"
              }
            ]
          }
        ],
        "msteams": {
          "entities": [
            {
              "type": "mention",
              "text": "<at>Lars Knoll</at>",
              "mentioned": {
                "id": "xxxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx",
                "name": "Lars Knoll"
              }
            }
          ]
        }
      }
    }
  ]
}

This works just fine and I get can see a proper mention in the adaptive card. When I press the Submit button, I simply resend the same adaptive card as an answer to the bot:

{
    "type": "application/vnd.microsoft.card.adaptive",
    "value": { ... same card as above ... }
    "statusCode": 200
}

I would expect that the mention continues to work, but instead I see “<at>Lars Knoll</at>” in teams (both Classic and the new Teams). In the web client things look slightly better (I don’t see the <at> tag and the name is highlighted), but the mention is still broken.

Is there a way to get this working or an ETA for a fix?