Version: (using Devel) Installed from: Compiled sources The tooltips are large and popup in a way that obscures the message view pane. To reproduce: Click a header to view a message. (one near the bottom of the header view). Leave the mouse on the header. Tooltip pops up, and covers part of the message, with no way to hide it via the keyboard.
Related to bug 182169. The important thing here: No way to hide the tooltip with the keyboard.
I'd prefer tooltips that just show what is hidden: When you hover over a closed group the tooltips are ok. But they get on the nerves and block the view when it comes to the messages. When the messages are shown IMHO the tooltips should be small and one-row to either show the sender's name (and address!) or the mail's subject when those parts are partly hidden, depending on where the mouse cursor points to.
*** This bug has been marked as a duplicate of bug 182169 ***