I was looking to try and calculate my opponent's score while I was in my development phase, to see if I could beat them (I couldn't, they were doing very well!), and tapped on a card to get a closer look. I then noticed the blue box appear around my park and hand, which allowed me to "take" the card from them. I could tell they were not my cards as they appeared smaller than my cards.

I had thought that maybe this was just a cosmetic issue, but I informed my opponent in the chat that I found a bug, started a screen recording, then confirmed my placed cards (including some of theirs). When the game scored, it scored the cards I had "taken" as if they were my own, but scored my opponent with their correct score (including their original cards).

Refreshing during the development phase reset the board (as it does normally), but I was still able to "take" my opponent's cards, and refreshing after scoring brought the images of my opponent's cards back, but the cards I had "taken" were still in my park- the cards seem to have duplicated themselves!

I screen recorded after having told my opponent I was about to do something stupid: youtu.be/oXU1GKAcSJw

You'll notice that I started with 20 cards at the beginning of the development phase, but ended up with 23 cards during scoring, and all of the ones I had placed in my park stuck around even after a refresh.

I first noticed this on mobile (Android, Chrome browser) but switched to a Chromebook to see if there was already a bug report for this, and I recorded on the Chromebook. I have yet to see if it happens again, but I will update this if I can do it again in another development phase.