The new *Kill Ring* buffer window will be replaced by the buffer you are working on

[c02y]

Say, you got only one window in the frame, and you type M-s l to complete a line, a new *Kill Ring* buffer window will be created, after you selected the right candidate, you hope to close the *Kill Ring* window, but it will be replaced the current buffer, so after you finish completing, you will get two windows.

[baohaojun]

The Kill Ring buffer is provided by browse-kill-ring.

What Emacs version and browse-kill-ring version are you using? Mine is:

Emacs: 25.0.50.1
browse-kill-ring: 20150104.1237 (installed from melpa)

And I can't reproduce the problem that you described.

[c02y]

Emacs: GNU Emacs 24.4.1
browse-kill-ring: 20150104.1237 (installed from melpa)
bbyac: 20150128.2119 (installed from melpa)

(Does it really need something like browse-kill-ring?)

This problem can not be reproduced easily in a simple file, maybe you should try it in a more complex one. Normally the candidates will exist in minibuffer, but I think when minibuffer is not big enough to show all the candidates, a new window called *Kill Ring* buffer window will be created to hold all ot them and this issue will happen.

I got a gif to show it (I'm using M-s l which is bbyac-expand-lines):