Withered Skeletons not spawning in/on Nether Fortresses

When in the nether on my world, I was looking for a wither skeleton in my nether fortress i found. I found the wither skeleton but they were spawned several blocks away from the fortress on an edge. I had to shoot them. Later on in that same area I found two more. I found none spawned naturally in or on the nether fortress. However, in 1.8 and 1.9 they would spawn properly in their fortress. Please fix this issue.