I’ve been working with Rob La Gatta on this issue and he suggested I post here, as this was an issue while beta testing that we’ve still not solved.
Our site is making heavy usage of Advanced Custom Fields (along with Roots Theme), particularly the Relationship field. Once TEC (basic) is activated, everything stored in the Relationship field disappears, both in wp-admin and on the front end. An example is the “Library” callout here (bottom right): http://um.bigdev.co/campus-life/um-life/. Once the plugin is deactivated, everything reappears, so it’s not actually overwriting anything in the database.
My team and I are at a loss as to how/where the calendar could possibly conflict with this field. Since we’re making so much usage of Relationships throughout the site, it renders 3.0 useless to us.
If you’d like for me to provide further details, please just let me know.
-Jared