I have learned this the hard way. Very irritating. Luckily Storyist, which I already own and receives updates pretty frequently through the App Store, works great. I imported my *.scriv file and have been running okay. I didn't know that three was ready but they were waiting for the Windows release; that is pretty uncool in my opinion. If they wait too long, I may just stay a Stoyist user and give up on Scrivener. From past experiences, beta and dev builds cause Scrivener all kinds of issues. So since I usually run those kind of builds to stay up on the latest stuff, I may have to give it up, sadly.
EDIT: So I spoke too soon. Storyist isn't working correctly either. Very strange issues while editing. Text disappears or doesn't and just stays there even when deleted. Weird lines and breaks show up. The only way to clear it up is to close the document and reopen it. So frustrating!