I was way too tired when I wrote the bugs. I've gone over what issues I had and answered you below. Hopefully this helps.
From the yt image thumbnail I believe. it was coming in as http on the page. As when I checked unsecure parts that image was the only part http. (Easily fixed it by changing the http to https is the xml file though)
Oh replication on this one!
With Ajax pagination on: switch between pages with videos on on the page you land on, They fail to load with playable image on them and click to youtube
With Ajax pagination off, The above does not happen and they load fine.
with it either on or off, if you enter a thread and post a video. The post will be added to the thread but the video within the post will not be playable and will take you to youtube if clicked until you refresh the page.
Seems to be an issue with ajax auto loading the posts in and the videos failing onto the non javascript backup, Logic wise that seems to be the issue.