I encountered this bug while I was playing around with the Warden, Dragon and just the snapshot in general. I found out when I killed the dragon ("/kill @e[type=enderdragon]") that once I put a warden through the end portal, it started acting all funny, the end credits scene started acting funny, I have a log sheet from the CLI as I am on Linux, but also a video.

Steps to reproduce the issue:

Going through the center End portal after the Warden goes through.