unthemed scrollbar, click-click-click-click-click-click on a scrollbar arrow-button does still trigger an unnecessary redraw at the opposite scrollbar button

Reproduction steps

• choose an arbitrary scrollbar, I used in my video the one of our notepad, but I tried others as well and they do behave the same (so it is not our notepad causing that, but most likely Win32SS)
• click quickly and repeatedly on one of the scrollbar-arrow-buttons

Observed result
It triggers an unnecessary redraw of the opposite button of that scrollbar, and therefore makes that one flash
0.4.14-RC-102-gd186a9f_gcc_4_7_2_dbg_lin__affected.webm
0.4.14-RC-102-gd186a9f_gcc_4_7_2_dbg_lin__affected.log (nothing gets logged)

Expected result
On Windows 2k3sp2 and XP no such flashing occurs, which makes me assume that it does not redraw that arrow then
2k3sp2_ok.webm