I've come across this same issue and got video of it. While I am running it in a Zur, Eternal Schemer brawl deck, I did not activate Zur's ability to turn it into a creature. You'll see it becomes a creature as soon as the enchantment enters play.

Edit: I can't seem to attach the mp4 file directly to this comment. So, here's a link to the video in Google Drive.

https://drive.google.com/file/d/134WS3ilrltyND3arSX0L9RizdXidV10Z/view?usp=sharing

Also same. Have won games I shouldn't've off of it attacking, and lost games I should've won based on it being interactable.

Same. Lost an otherwise won game in which my opponente interacted with it with a Dreadbore.
Lost a trophy and all the benefits of a 3-0 Traditional.

This is a key card to specific deck deisgns and they fall appart if the opponent can use creature destroy spells on it.

Came to report the same thing. I would not have drafted the deck that I did knowing this bug exists, as Starfield is a key component of my long term strategy and it should be difficult to remove in best of 1. Now, it's not.

Came to report the same. Starfield turns itself into a creature as soon as you control 5 enchantments. It shouldn't animate itself at all.

Came here to comment the exact same thing! I just lost a premier pioner draft because of that. Starfield made itself into a 5/5 and my opp killed it with creature removal.

This also occurred in my game (to my benefit, in my case, but it shouldn't happen).