I started a new survival game in Minecraft 13w37b and spawned in a Plains biome with a small Sunflower Plains biome next to it. After sleeping in my bed I found skeletons that weren't burning in the middle of the plain: they somehow found protection from sunlight with Sunflowers. Pushing them out of the Sunflower's hitbox was enough to set them on fire, and they puposedly return to the Sunflower as they detect it is a safe spot.

Steps to Reproduce:
1. Find sunflowers or other two blocks high plants, or plant them in a well-lit area.
2. Wait for night
3. Wait for undead mobs (skeletons and/or zombies) to spawn close to the sunflowers
4. Wait for dawn
5. As soon as the sunlight level is high enough to set undeads on fire, they will seek refuge to the nearest safe spot, including sunflowers and .