yank-pop broken in current dev zsh?

[Bart Schaefer <schaefer@brasslantern.com>]

zsh-5.2-67-g424b417 (haven't checked older ones, but I don't know of any
very recent changes that would affect this):

If I start (zsh -f, emacs bindings) with

% echo one two three

and I execute ESC backspace ctl-space ESC backspace, I have

% echo one 

(with trailing space) and the kill ring contains "two " and "three".  If
I now execute ctl-y ESC y (yank "two " then yank-pop to get "three"), I
end up with

% echo one three

with "thre" highlighted and the cursor on the final "e".  The cursor should
be after the entire word "three", should it not?  The whole "three" is then
removed/replaced on a subsequent yank-pop, but the highlighting and cursor
may be off by one on the next (and all following until I cycle all the way
back to "
two ") replacement as well.

I at first thought this was related to setting the mark, but that isn't it.
It also doesn't seem to be related to yank-popping a shorter word after a
longer one.  It doesn't always happen, though it is repeatable via the
example above.

I suppose this might be related to the CURSOR increment I mentioned needing
following select-in-shell-word in a widget.