There are no updates for Beta 2.
You're probably seeing one of two issues with the latest nightly build:
1) playerglobal.swc change http://forums.adobe.com/thread/559312?tstart=0
2) Namespace change from xmlns:mx="library://ns.adobe.com/flex/halo" to xmlns:mx="library://ns.adobe.com/flex/mx"
Jason San Jose
Quality Engineer, Flash Builder
I've tried this workaround but Design mode still doesn't seem to work.