Not a bug
BYOND Version:511
Operating System:Windows 10 Home
Web Browser:Chrome 57.0.2987.133
Applies to:Dream Maker
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.
Descriptive Problem Summary:
Animating an icon larger than 32x32 which has empty pixels causes the bottom left part of the icon to fade in and out. (note that this glitched part of the icon is the actual position where its located on map)

In this case, I tried animating a lightrays icon. It created a weird glitch at the bottom left part of the icon. (See screenshot)
Numbered Steps to Reproduce Problem:

Code Snippet (if applicable) to Reproduce Problem:
parent_type = /turf
icon = 'light_source.png'
layer = 200
density = 0
animate(src,transform = matrix(), alpha = 170, loop = -1, time = 10)
animate(transform = matrix(), alpha = 255, time = 10)

Expected Results:
animating nicely without causing the bottom left icon to look weird.
Actual Results:
glitched out icon


UPDATE: After changing the parent_type to obj. It worked fine! Seems to be a bug for turfs.
I doubt there's actually a bug in play. This smells like a mistaken assumption about stacked turfs.
This smells like a mistaken assumption about stacked turfs.

It is.


You can only have a single turf at each location on the map. Any turfs underneath a partially transparent turf are actually added to the underlays of the topmost turf.

Underlays are not stored as objects. Only appearances are stored in the underlays and overlays lists. So your floor turf doesn't really exist except as a part of the LIGHTSOURCE turf you layered on top of it.

When you changed the alpha of the LIGHTSOURCE object, you also changed the alpha of all the underlays of the lightsource object.

Also, turfs larger than TILE_WIDTHxTILE_HEIGHT only ever actually occupy a single space on the map. movable atoms have special behavior that allows them to span multiple turfs. This explains why it only affects the bottom-left turf underneath your lighting object.

Not a bug. Intended behavior.
Lummox JR resolved issue (Not a bug)