GeDialog docked in C4D's layout receives a call to Command() with ID 92, when user clicks the little x in the window title. I tested this in R21 to S24.
Other ways to close a dialog do not show this behavior (i.e. close button of floating dialog or "Close Manager" from the hamburger menu of a dialog).
Not a big deal at all. I'm just wondering, what may be the reason or if it might be a small bug?