Probably a duplicate, couldn't find the original. To reproduce, place a mob/player head other than a skeleton skull, watch as it very shortly will be displayed as a skeleton head.
MC-65911
Skulls shortly display as skeleton skulls when placed
Resolved
Duplicate
0
(Unassigned)
Unconfirmed
head, mob, placing, skeleton, skull
Minecraft 14w32b
Retrieved
Dupe of MC-52802, which will be fixed for 1.9