ID:2518213
 
BYOND Version:512
Operating System:Windows 10 Home 64-bit
Web Browser:Chrome 78.0.3904.70
Applies to:Dream Maker
Status: Open

Issue hasn't been assigned a status value.
The map editor seems to render transform incorrectly.

Demo
From left to right: normal, horizontal flip, vertical flip, both flips. Flipped icons are incorrectly positioned and part of the icon is cut off.
obj/test
icon = 'Icon.dmi'
icon_state = "test"

// These can also be made as instances in the map editor.
vertical_flipped
transform = matrix(1, 0, 0, 0, -1, 0)

horizontal_flipped
transform = matrix(-1, 0, 0, 0, 1, 0)

flipped
transform = matrix(-1, 0, 0, 0, -1, 0)

Same result in 513.
This appears to be an artifact from the software rendering mode. It'll be eliminated completely once I eventually switch the map editor over to standardized rendering.