SharePoint 2013 Preview Popup Menus Missing

After re-installing SharePoint 2013 Preview to fix an issue on a test server, I found that the popup menus (such as the settings menu at the top right corner) did not work in IE9. Those areas did not change background colour, either, when hovering over the location. Yet they worked in FireFox! Eventually I removed the server name from the local intranet zone in IE - and the menus started working again. Tried replicating the issue by adding the URL back to that zone, but can't get it to happen again. Beware!