Skeletons sometimes spawn as normal from egg in Nether

Fooling around in the nether with skeleton eggs. Off screenshot it spawned as a normal skelly, then it was a wither skellybutt. I tried more and found that the bags of bones spawn rarely normal in the nether. Im not sure if this is a bug or not.

Steps To Reproduce:
1.Go to the nether
2. Get Skeleton Eggs
3. Spawn a Skeleton

Thanks!