Wow, 10049 is a bit of a regression. Spartan is surprisingly feature-incomplete. Lots and lots of stuff doesn't work (syncing and default tabs being two things), and while I'm sure it will be nice one day isn't much of a preview version.
But, more important, things are very unstable. Touch in particular is problematic--in a number of apps (Spartan, IE at least) some on-screen elements just don't respond to touch. Had to switch to the keyboard to even enter this site's URL to come here. It's pretty wonky switching in and out of tablet mode. Seriously, just messy.
Really wishing I'd stayed with 10041 for now, but at least it's looking like we won't have to wait too long between builds.
Edit: Okay, did a two-button shutdown, and the touch issues went away. So, I suggest doing so.