I'm very sorry you're having trouble with the new videos.
For an immediate solution, try clicking on the "HD" button in the video player control bar. This will switch video playback from Microsoft's IIS Smooth Streaming to standard MP4 playback. With the HD MP4 playback, the video will continue to download when paused, so you should be able to download the complete video and play it back without buffering problems.
Smooth Streaming, on the other hand, only delivers chunks of video as you view them. That means a paused Smooth Streaming video will not continue to download when paused. The advantages of Smooth Streaming are that you can instantly skip to any point in a video and you should be able to enjoy near instant playback on most bandwidths. We'll work with our video delivery network to make sure the experience is optimized to prevent the buffering you're seeing.
I hope that helps. If you have any trouble, please let us know.