@Dave S I was moving controls around in a window, and all of a sudden the ADD EVENTS window opened..
Maybe you clicked to select, then clicked to drag too quickly.
It has seemed like Xojo's double-click fires differently from the rest of the OS. Maybe the second click is timed from after the selection is complete(click handler end) rather than from when the actual click occurred(click handler begin). So if there's a lag in the selecting of controls, double-click is fired incorrectly on a second click.
I've developed a habit of click... wait.. wait... then click again when working in Xojo.
No idea about the window resizing thing though.