bug#19988: 25.0.50; Drag events ending in different frame

[martin rudalics <rudalics@gmx.at>]

 > The typical scenario where I run into it is trying to select text
 > using the mouse and inadvertently moving the mouse slightly outside
 > the frame.  The region stays selected, even as the mouse is outside
 > the frame, so I think all is well.

You _have_ to move outside the frame if you want to scroll the text in
the window and thus enlarge the region.  If the mouse cursor remains in
the window, text won't scroll.  All applications behave like this.

 > But as soon as I let go (release `mouse-1'), the selection disappears,
 > and point moves back where it was - where mark is now set also (empty
 > region).

Because you should move the cursor exactly to the location where you
want `point' to be.  Any position of `point' when the mouse cursor is
outside the frame is specified only by a previous position and the
amount text scrolled.  Emacs is different here because the region cannot
exist without `point'.  Other applications can leave the selection alone
because their equivalent of point doesn't change during mouse dragging.

martin