i am also experiencing this in 15w33c, however the world was generated using a previous version.
thus far i have 100 or so zombies from a single spawner and none of them are a variant.
edit: only way i was able to reproduce in lab is generate the world in 1.8, and upgrade to 33c. The spawner then produced no variants. When i upgraded that same world to 34a the spawner began working again, so it looks like all should be well next update.
can confirm, changed from 9 to 16 chunk render distance and experienced what is shown in youtube video.
changing back to original render distance removes glitchiness
still present in 14w28a
can reproduce as well, worth noting dogs will not tp to player either, although they respond to sitting.
http://gfycat.com/FaintTatteredAnglerfish
Video showing bug in action. Attached .webm also.
can confirm overabundance of skeleton traps when surrounded by an ocean biome.
pictured are some traps after one thunderstorm
http://i.imgur.com/GKwRQOt.png