ID:2025641
 
Not a bug
BYOND Version:510
Operating System:Windows 8 64-bit
Web Browser:Firefox 43.0
Applies to:Dream Seeker
Status: Not a bug

This is not a bug. It may be an incorrect use of syntax or a limitation in the software. For further discussion on the matter, please consult the BYOND forums.
Thia is a bit of a weird one. Overlays seem to either end up going below or above everything else on the plane depending on if a plane master is present.

I'll drop in some more info when I figure out what's going on
This partially seems to have to do with me trying to use a screen object to fill in a "background" for the plane. Not sure how you're supposed to do this with the new HUD layering rules.
Seems that even using a normal object at layer 20, the overlays of a lower object just go above everything anyways, even though the main object is far below.
Use BACKGROUND_LAYER or a negative plane.
Plane masters can't cover multiple planes.
They can handle pseudo-planes line BACKGROUND_LAYER, though.
That sadly limits me to either placing whole-plane operations either below or above the whole thing, could be somewhat limiting.

Either way, the problem here is that overlays seem to layer basically however they want within planes - even above HUD objects (wedging those inbetween the "main" object and the overlay). Not even KEEP_TOGETHER seems to help.
Can you give me an example of how the overlays aren't working? Any kind of test case to look at?
image/fuck
appearance_flags = PLANE_MASTER
plane = 2

mob
Login()
..()
src << new /image/fuck(loc=src)

obj/test
icon = 'test2.dmi'
plane = 2

New()
var/image/O = image('test2.dmi', "foo")
O.pixel_x = 4
O.pixel_y = 4
var/matrix/M = matrix()
M.Translate(-2, -2)
O.transform = M
src.overlays += O

obj/test2
icon = 'test2.dmi'
icon_state = "foo2"
plane = 2
layer = 20
blend_mode = BLEND_ADD


If "foo2" is green, "" is red and "foo" is black, this produces yellow for some reason. It seems the overlay is just going under everything in this case, but I've had it appear pretty much wherever it wants.
I tried out your test and was able to figure out the problem: The image you added does not have the same plane as the parent object.

Planes aren't inherited, so that's why. I suppose I can see some justification for inheriting when plane=0 though. That's something I should consider.
Lummox JR resolved issue (Not a bug)