usually when editing apps i'm zipping around my mac pretty quick (perhaps sloppily), and when i go to select all text in a popup from the inspector it always closes the popup unless i let go at just the right point inside the popup on the mouse up event.
i think this is a bug and it should close the popup when you click outside the popup instead of click down, drag outside, and let go.
here's a video, it's wickedly annoying:
It can really slow things down.