With Emacs 25.2 under MacOS 10.12, I use a mouse key that has bindings on
both its depress and release states.  The depress is in a frame with 2
windows (one showing *Buffer List* and the other showing hmouse-drv.el).
The depress occurs in the *Buffer List* window.

The release occurs in another frame and the release window is showing
hui-window.el.

Here is the drag event generated.  Element 2 shows the proper depress
window but element 3 shows the depress frame rather than the release
frame.  And element 3 has a frame rather than a window as its first
argument even though the Elisp manual says it should be a window.

(drag-mouse-2 (#<window 90 on *Buffer List*> 2905 (88 . 467) 4050744642 nil
2905 (12 . 33) nil (4 . 5) (7 . 14)) (#<frame hmouse-drv.el
"/Users/bk/Dropbox/emacs/hyperbole/" 0x102f5bde8> nil (-1373 . 463)
4050749802))

Has anyone seen this behavior before or know what's going on.  I'm just
trying to write a simple function that selects a buffer from one window and
puts it in another window which may be in another frame.

Thanks,

Bob