It sounds like they have broken something in the browser control in the Beta. They had a similar problem in earlier versions of CC 2015 that they later fixed.
I'm afraid there isn't much we can do about it other than to report it to the Dreamweaver team and hope they fix it. Last time it was a MAC only issue. I'll download the latest beta and test it on PC and mac, but my bet is that this is a bug in the MAC version of the Dreamweaver beta.
Please report the issue to the Dreamweaver team as well:
Issue is: "when an extension uses the dreamweaver browser control it won't populate textarea or input type="text" form elements and crashes often"
I'll report it as well once I get more information.