Affects Version/s: Minecraft 1.11.2
Fix Version/s: None
Environment:Java 8 Update 131, Java SE Development Kit 7 Update 4, Java FX 2.1.0 SDK , Java FX 2.1.1, Windows Vista Home Premium 64 Bit with Service Pack 2, Intel (R) Core(TM) i7 CPU, 920 @ 2.67 GHz, 6 GB RAM
The bug for Wither Skeletons 'dancing' / flailing their arms exists in Minecraft PC 1.11.2 . This can actually be provoked in methods involving the Wither Skeletons attacking entities other than the player, and hence can be performed in Creative Mode.
I have tried four methods to provoke said bug, with interesting results. Sorry if the video quality is poor, Hypercam isn't the best, and note the cake in the videos posted below was added for humor and does not relate to the bug (On a side note not pertaining to the bug, Wither Skeletons 'dancing' in the prescence of cake would be a hilarious feature).
Method One: Cage: https://www.youtube.com/watch?v=rJOIGXwX-UA
Method Two: Spawn in Slabs: https://www.youtube.com/watch?v=dR3N52G_Kko
Methods Three and Four: Minecarts and Boats: https://www.youtube.com/watch?v=-OORhTyEA1M
So the idea here is to cage up an Iron Golem and spawn Wither Skeletons in different fashions. Methods three and four using Boats and Minecarts will have the Wither Skeleton 'dance' indefinitely so as long as the Iron Golem stays alive and they stay in their boat or minecart. Simple and easy to replicate.
Methods one and two are a bit more interesting. Method one involves caging up an Wither Skeleton with an opening door consisting of End Rods and Sticky Pistons, and putting an Iron Golem in another cage, right across within viewing distance of the Wither Skeleton.
Method two involves spawning Wither Skeletons in slabs as seen in the video above while the Iron Golem is caged.
The interesting thing about methods one and two is the Wither Skeletons will 'dance' for an undetermined/random amount of time if left alone until the World (And I say this for a reason) itself corrects itself and the Wither Skeletons stop 'dancing' and outright try to attack the Iron Golem.
It seems when the World corrects itself on this matter, any more Wither Skeletons spawned in will immediately try to attack the iron golem as normal and will not 'dance' and the glitch can no longer be performed with methods one and two in that world again, meaning if a player would want to recreate the glitch using methods one or two, they would have to create a new world to do it again.
Alternatively, The world may correct itself sooner with methods one and two if the player either bumps the Wither Skeleton, or completely destroys the structure the Wither Skeleton was spawned in.