here as well, been working in a nether fortress for a week - never seen a wither skeleton and blazes only spawn around spawners.
related? MCPE-16038
Note - Pigs can fly isn't translated in either language.
I made a comment but removed it after some testing - confirming a bug where slime block and sticky pistons can move a comparator but not a repeater.
I've had this happen in 0.15 on one of the realm servers. But I think it's an outstanding bug also in PC. If a ghast is spawned inside the walls, then it can "see" players through solid blocks and will keep firing at your direction until it broke through.
See also:
smelt cobblestone with coal is ok in Win10 0.15.2
still crash on Win10 0.15.2
if this is a fix to allow wither skeleton to spawn in fortress crossroads, can we look at witch spawn in witch huts too?