Wither Skeletons don't attempt to hide from sunlight, but once they get under an overhang, they don't move out from under it, not even to attack a player.

Noticed in this video (at about 29 minutes in): https://www.youtube.com/watch?v=HMs0eIayCKE
It was recorded in 1.8-pre1.

Tested further by myself in 1.8-pre2. They came out from under the overhang a few times, but most of the time they didn't. They came out about 18% of the time (7 times out of 40 tries).
I will upload a screenshot of my testing apparatus if requested.

Relates to MC-8671, which is fixed.