"Scrolling by pressing the scrollbar arrows does not draw the arrows as pressed"
Fixed by a patch of JIRA-user 'I_kill_bugs'. Thank you very much!
The regression was introduced by 0.4.11-dev-586-g
929a2c6637
(which itself aimed to fix CORE-13986,
but not CORE-13918 as erroneously stated in commit comment)
I intend to port this back into 0.4.13-RC later.