One feature that has been requested by a number of customers for our Docking/MDI product is to be notified of when a tool window that is auto-hidden flies out or back in, such as the Error List tool window in the screenshot below:

We just completed adding two new events to DockSite named WindowAutoHidePopupOpened and WindowAutoHidePopupClosed.  Each even passes an event args that specifies which tool window is being opened or closed.

These new features will be available in the 2014.1 version of Docking/MDI.