helm bu(https://github.com/syl20bnr/spacemacs/issues/7446)

helm-core_helm.el

(defun helm-persistent-action-display-window (&optional split-onewindow)
  "Return the window that will be used for persistent action.
If SPLIT-ONEWINDOW is non-`nil' window is split in persistent action."
  (with-helm-window
    (setq helm-persistent-action-display-window
      (cond ((and (window-live-p helm-persistent-action-display-window)
                (not (member helm-persistent-action-display-window
                      (get-buffer-window-list helm-buffer))))
              helm-persistent-action-display-window)
        ((and helm--buffer-in-new-frame-p helm-initial-frame)
          (with-selected-frame helm-initial-frame (selected-window)))
        (split-onewindow (split-window))
        ((get-mru-window))
        (t split-window (get-mru-window nil t))))))