I see now that you are referring to the dumb mobs being given an AI again as the actual bug, to that I agree with you somewhat.
They should stay dumb, on the other hand, we should always treat the mobs with respect whether they are dumb or not, (i.e. don't rest your life in the hands of a dumb mob)
There isn't an easy way to fix this, the only way is to write a new part of the /spawner plugin that adds a tag to the spawned entity(mob) so that it can be differentiated from normal entities when the map is saved,unloaded,loaded, etc. I think the current trick is just making the mobs think they are in peaceful mode, but I don't think there is a way to save the individual mob states after they are spawned, like... you can spawn them in and trick them into thinking its peaceful mode, but you can't save the data to include their last thoughts, when the chunk is reloaded it just goes through the normal AI surroundings check, you would have to make all mobs dumb on the whole world all the time in order to counter this.
I do not know if entities can have NBT tags or if it would require an actual mod to add "duplicate" mobs with no AI, then the spawner would just be spawning custom mobs.........doubt its going to happen.
And if it does, I want mini-ghast-named-timmy spawners.