Guardians not spawning on superflat worlds

I'm new here, but i can confirm this.
I have been messing around in superflat mode with the biomes set to deep ocean with ocean monuments spawned evereywhere, but guardians just won't spawn.
I have been trying to use ocean monuments for use in a survival map, but this kinda a big wrench in my plans.

Confirmed for 14w34d.

Confirmed in 1.8.1-pre3. Repro steps:

1. Create New World
2. Game Mode Creative
3. Seed: NoGuardians
4. World Type: Superflat
5. Customize to preset: "Water World"
6. Generate Structures: ON

You will spawn near a monument at X=1200, Z=-200. Explore the temple (Respiration Helmet and Night Vision potion recommended). You will find Elder Guardians (spawned in with the structure), but no normal guardians will spawn, only squid.

Not a dup, but possible connection to MC-3524? (Witches do not spawn in superflat worlds).

Note, this is also reproducible in a normal world by editing the map type. Repro steps:

1. Make a new, normal world in creative mode
2. Seed: 202961
3. Note the monument near spawn, X=-350, Z=150
4. Guardians will spawn when on Normal difficulty
5. Switch to peaceful and exit
6. Open the "level.dat" file in NBTExplorer.EXE
7. Edit the Data > "generatorName" value to a value of "flat"
8. Save and exit, and re-load the world in Minecraft
9. Switch back to Normal difficulty, no guardians will spawn

You can edit the type back to "normal" and Guardians will begin spawning again.

Please fix! I need this for a custom map!!

Still an issue in 1.8.2-pre7

Confirmed for 1.8.4. I finally know why they weren't showing up....

Still an issue in 1.8.8 and the newest 1.9 snapshot 15w45a

Can confirm.

OK, good news everybody; I figured out the technical cause of this issue. You might want to put this explanation on the original report (With credit if you want 😛), but here's what I found the cause of it is;
The NBT file Monument.dat, which is in the data folder of the save file, has information about all the monuments spawned in a world, but not only that, it also controls spawning of guardians in this way; There is a list tag called "Processed", which, in non-flat worlds, has 16 compound tags, each one containing two integers; One for X coordinate and one for Z coordinate. These are actually chunk coordinates, not block coordinates. These coordinates control in which chunks guardians should spawn. However, the bug goes like this; In superflat worlds, the Processed tag is actually empty, meaning there are no chunks that guardians can spawn in. (Apparently this is wrong. The Processed tag does not, in fact, control the spawning of guardians. The true reason in the following one.) Also, another reason to this bug (As Brad Corbin said (Also credit 😛)), for some reason even if there are chunks listed there (If you add them manually), it still won't work if in the level.dat file the generatorName is "flat".

More good news, kind of related to that; Using this information and any NBT editing program, you can actually fix this issue (Which is exactly what I'm doing for my upcoming adventure map).

I also put this information on the wiki.

Confirmed for 1.9.3-pre3

Confirmed for 1.10.

Confirmed for 1.10.1.

Affects 1.13 "Aquatic Update"  I would think by now this would have been addressed considering 1.13 is so much about the water. Please consider how many are wanting to start a new water world, yet only to find ocean monuments that don't spawn guardians.

Confirmed for 1.13.1.

Confirmed for 1.14 Pre-Release 2

Confirmed for 1.14

Testing regarding this issue, this bug is superseded by issue MC-169728