Tooltips will be back in the next version. Thanks for reporting.

The new preview window has apparently lost a feature that it used to have, which is a hover tooltip that shows the window title. If I have both Outlook and a message window open, I see two Outlook icons in the desktop. In the previous version, if I hovered the mouse on one of them, it would show me the window title. I sometimes drag windows to other desktops from the preview window, and I would use that feature to be able to tell which window I needed to drag.

This is more of a problem with the "icons" representation. The "Window sketches" representation doesn't have this problem.