I also ran into that issue and fixed it in master; please pull again and it should work. (Update: since my commit the define name has been changed to LV_THEME_DEFAULT_DARK and the number was inverted.)
It might be a limitation of having a 1-pixel thick needle, as I can’t think of a simple way to keep the thickness equal between angles that are multiples and not multiples of 90 degrees. FWIW I’ve seen this issue occur in browsers as well when rotating images.
The best workaround is probably to use a thicker needle so the effect is less obvious.