Like I said earlier you will have to look into youtube CDN's at some point and maybe bounce some using your firewall. There will be some googling involved. Or at least start with a minimum of see how it is affected if you use some alternative DNSs.
Btw, have you discussed the youtube situation with slingshot? It might take a couple of attempts but someone may look at in detail. It can happen.
I know how it works at Slingshot with regards to investigating a fault. In my case, they won't see this as a problem on their end. In their defense, it probably isn't. What I think it happening is the video is sourcing from an overseas server and upon refresh it comes from a CallPlus server. Not sure if that is because CallPlus cached it in the 5 seconds it takes me to refresh like how it worked with Telecom's BigTime, or if YouTube decides there is a more suitable server for me to be connecting to. YouTube is still amongst the services cached along with Steam and popular torrents.
Not sure what a CDN is. I'll have to Google that one. :)
EDIT: Content Delivery Network. I've already blocked one or more I think by mistake. I'll have a look in to it and report back :)
Sometimes what you don't get is a blessing in disguise!