I did not have this problem during the beta but it’s an issue in the official release as of now.
When I play big files the image starts to lag after some time and the image only appears to refresh when a new row of subtitles are displayed. It’s like the video framerate and subtitles are somehow synced. The audio is fine, it continues to work and in sync.
I am streaming files from my Apple Time Capsule and it worked perfectly during the beta. I have checked the internet connection and therein lies not the fault either, I have a solid 100mbps connection.