It's preventing the buffer from automatically shrinking
"Show which-key buffer when popup type is side-window."
(let* ((side which-key-side-window-location)
(alist '((window-width . which-key--fit-buffer-to-window-horizontally)
- (window-height . (lambda (w) (fit-window-to-buffer w nil 1)))
- (preserve-size . (t . t)))))
+ (window-height . (lambda (w) (fit-window-to-buffer w nil 1))))))
;; Note: `display-buffer-in-side-window' and `display-buffer-in-major-side-window'
;; were added in Emacs 24.3