bug#16748: restoring a frameset duplicates existing frames

[Glenn Morris]

Package: emacs
Version: 24.3.50

Current trunk on GNU/Linux under X:

emacs -Q
C-x C-f 1
M-x make-frame
C-x C-f 2
;; Now we have two frames, one visiting "1", the other "2".
;; Save to register "a":
C-x r f a

M-x make-frame
C-x C-f 3

C-x r j a

This iconifies the existing frames 1, 2, 3, and creates new frames
visiting 1 and 2. These are identical to the ones that previously
existed, so why did it create new copies?
M-x frame-configuration-to-register does not duplicate existing frames
in this way, it simply iconifies frame 3.