The problem is, people know how to spawn him (check his page at the bottom) and also know how to spawn Quillmane.
Before, people used to kill everything trying to spawn Quillmane and this lead to the placeholders for many of the named mobs being killed and then the named mobs would pop.
Since everyone knows how to make Quillmane spawn, no one is killing the Undead Cyclops ph anymore so he isn't spawning. Follow the instructions in the wiki and you'll get him to spawn. I used to make sets of Ro armor so I can verify it works.
Unless you spawn him and follow him around and determine for sure whether his pathing is classic or not, I don't believe there is any bug.
http://wiki.project1999.com/An_undead_cyclops