Sidebar Blocks are Not Reusable
In < RC 2, this only presents when using sidebar blocks on non-wiki pages with the vBulletin CMS widgets system or another widget system like [bd] Widget Framework. If you decide to put duplicate Javascript-enabled blocks on such a page, only the first instance of the block will be enabled.
Fixed in the next release. AFAIK, this affected the search block and the activity feed.