The title bar of my Finder windows looks like this:
If I click on the large-font path, or anywhere to either side of it, and drag, the window drags as usual. But if I click on the small-font path and drag, the window disappears and I find I’m dragging a miniaturised, semi-transparent version of the window, which expands to full size when I let go.
It’s vaguely disconcerting. Does it serve some useful purpose? I confess I’m not terribly sure why the small-font path is there at all. (The black icon is NameMangler, which I don’t think is relevant.)