Newell Henry Clark

So in other words, the issue is that, after failing to pathfind to the nearest block, the bee doesn't remember the blocks that it failed to pathfind to when choosing which block it should pathfind to next?

Can confirm. My wither skeleton farm in the soul-sand valley isn't spawning any mobs. I would recommend not updating until this gets resolved. 

Please strongly consider leaving this the way it is, at least for redstone dust. It's a huge pain to build redstone circuits in the nether when mobs can spawn on the redstone dust. There are some circuits where it is not possible to place a block over the dust (for example, when propagating a signal downward using torches and dust, the two blocks above the block supporting the dust are occupied by the dust, and the torch immediately above it). 

Having to work around mobs spawning on redstone dust when building in the nether is unnecessarily limiting. Also, to whoever suggested putting redstone dust on glowstone, that won't work if you need the block to be powered (as with the downward torch tower I already mentioned). 

As for the other blocks mentioned, repeaters and comparators have a solid hitbox, so mobs shouldn't be able to spawn on them regardless.