ess-eval-line-visibly-and-step splits window and shows in both

Question

I've noticed that when I execute ess-eval-line-visibly-and-step inside an R-mode buffer and I don't already have an active R session, it will split the screen (good), however it will show both sides of the split into the R session (bad). I would expect it to split the screen and show the R session on one side (ideally the right) and leave the R-mode buffer on the other side (ideally the left).

The only bit of my init.el referencing ESS is

(use-package ess
  :ensure t
  :defer t
  :config
  (setq ess-ask-for-ess-directory nil        ;; just run R wherever
                                             ;; the file lives
        ess-history-file nil                 ;; don't save history
        ess-eval-visibly-p nil               ;; when running R, don't
                                             ;; show code, just output
                                             ;; (greatly speeds
                                             ;; running)
        inferior-R-args
          "--no-restore --no-save --quiet"   ;; R startup conditions
        ess-style 'RStudio                   ;; better indenting
        comint-scroll-to-bottom-on-input   t ;; force ESS to scroll R
                                             ;; to the bottom after
                                             ;; running code
        comintq-scroll-to-bottom-on-output t
        comint-scroll-show-maximum-output  t
        comint-move-point-for-output       t))

I've commented out all the setq and it doesn't fix the issue.