Once shielded from sunlight, Wither Skeletons will stay put most of the time

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.