It's been reported in a few threads, like this one: http://www.zimbra.com/forums/general...n-zd1-zd2.html.

We have tracked down the issue and fixed it in this bug here: Bug 52712 – trouble importing data from 1.0 to 2.0.

So please hang on to your exported local data from ZD 1.0. Once ZD 2.0.1 is out, you should be able to import them back.