Yeah, the forum code upgrade to v3.3 was a major code upgrade and not all the customizations and enhancements were compatible. Rather than postpone the security upgrades, I decided to just disable the customizations and enhancements that were not compatible with the new code and address them later. The auto-parsing of URL's was one that I had to disable. As a stop-gap, I just added a "youtube" BB code tag you can use for now. ie, [youtube]video url[/youtube] will embed it.
EDIT/UPDATE: I fixed it. Should auto-embed youtube links again now.