I deleted all the downloads that I had started before the update and the problem seems to have gone away.

The video files still freeze but after a few seconds of being frozen LW opens a dialogue box telling me the file is corrupted and asking if I want to continue downloading.

I've tried with two video files (with a lot of hosts) and happened on both. The videos turned out to be fine, so it must be a small corruption (like the ID tag or something)