Ghasts spawning in PS fields

[Th3Element05]

I have a platform in the Nether with 4 diamond blocks protecting it, all of them currently have prevent-mob-spawn enabled.  Yet ghasts keep spawning on and around my platform.
I am in the area above the Nether, and since bedrock is a non-spawnable block, they shouldn't be able to spawn above it.  And all of the spawnable surfaces that I have placed are covered by my PS fields.

[Th3Element05]

Thank you, Lovely 

I want to note here that it is possible that these ghasts are spawning just outside of my ps fields and some of them are just floating in closer before they shoot at me and I notice them, but as far as I know, they shouldn't spawn above bedrock blocks.
I'll try to do some tests to isolate wether or not they are spawning in my fields, or just above the bedrock outside of them.

[roadkilered]

We have had a clan set a base up above the bead rock, only to be attacked constantly by ghats. I think they are spawning outside the field.

[Th3Element05]

Ghasts spawn conditions are:
Any light level, in any 5x4x5 space above a spawnable block.

Non-spawnable blocks include things like water, half slabs, glass, etc.  It is my understanding that bedrock is also a non-spawnable block, and mobs cannot spawn on it (otherwise, the upper nether would be crawling with all kinds of mobs, not just ghasts).

I have covered every spawnable block in the area in question with glass, definitely a non-spawnable block.  I will let you know if ghasts continue to spawn within, or near, my ps fields.
If they do not continue to spawn, then I can confirm that they are not spawning above the bedrock (and that it is a non-spawnable block), and from there infer that they must be spawning within my ps fields, and hopefully we can figure out what is going on from there.

[roadkilered]

i guess as long as you don't place a spawn-able block outside the ps field you will be fine. That explains why ghasts were attacking the other clan. They had placed blocks that Ghasts could spawn on.

[Th3Element05]

I haven't seen a ghast since I placed all of the glass.  I don't know why the ps field isn't preventing the ghasts from spawning...

[Th3Element05]

I have a theory.  It is purely speculation, but...

Let's presume that the code in the Precious Stones plugin uses the light level requirement for hostile mobs to spawn in order to prevent-mob-spawns.  With the flag enabled, it would treat the area within the PS field as having a light level too high for hostile mobs to spawn (8 or higher).  But Ghasts can spawn in any light level, they just need enough room above a spawnable block.

I have no idea how prevent-mob-spawn actually functions, so I'm just guessing.

[bknysnake]

nope because animals such as pigs/cows/sheeps spawn above ground in the day light, yet PS does prevent them from spawning I've even tested this with spawn eggs, haven't tried it with ghast.