Wither Skeletons NOT spawning in pre generated fortresses

No longer getting wither skeletons on fortresses I've previously found them at (have 3 skulls from them). Not sure when this stopped happening (more worried about my white sheep at 1.0.8 heh), but spent hours half slabbing in and around a fortress and didn't see one wither skeleton, lot's of blazes, but no withers 😞

I did notice this line on the offical release log of 1.0.0 "(Guardians, wither skeletons & blazes respawn naturally again when switching from peaceful game mode to easy/normal/hard; however, they will only do this in newly generated structures, not ones that have already been discovered.)"

I know this has been reported and duplicated many times. (See MCPE-16292 for a list of others), but the Blazes spawn fine (not just at spawners). I have NEVER switched to peaceful mode on my realm (might have switched between easy, normal and hard), but if the blazes are spawning, why aren't wither skeletons. Even IF it's the case that switching from peaceful stops them forever... What? Why? That's a bug/issue! As I said never switched to peaceful (it's cheating IMO!) 🙂

If this is a feature, and I have to find a 3rd fortress, and it happens again... grrr.. 😞