Resolution: Works As Intended
Minecraft 1.8.1-pre4, Minecraft 1.8.1-pre5, Minecraft 1.8.1, Minecraft 1.8.2-pre1, Minecraft 1.8.7, Minecraft 1.8.8, Minecraft 15w36b, Minecraft 15w36c, Minecraft 15w38b, Minecraft 15w46a, Minecraft 15w47a, Minecraft 15w47b, Minecraft 15w47c
1) Summon an Ender Dragon.
A very glitchy, rapidly vibrating Ender Dragon should result. This is likely caused by the way that the Ender Dragon turns. Relogging fixes the issue, but the Ender Dragon will be completely straight and always face North.
This does not occur with any other mob.
This seems to be closely related to my other report,
MC-74114, since once this issue is fixed by relogging, the dragon no longer takes damage.