ID:2517001
 
Resolved
Regression (512.1488): The behavior of mouse pointers changed inappropriately, preventing drag cursors from working.
BYOND Version:512
Operating System:Windows 7 Pro 64-bit
Web Browser:Chrome 77.0.3865.120
Applies to:Dream Seeker
Status: Resolved (513.1491)

This issue has been resolved.
If you have mouse_pointer_icon set to an icon, mouse_drag_pointer doesn't have any effect. 513.1490.
I need a test case for this.
In response to Lummox JR
Here is a snippet like you asked on Discord:

client
mouse_pointer_icon = 'cursor.dmi'//Make an cursor icon with only the default state, without a drag state

obj/dragtest
icon='X.dmi'//any icon
New()
..()
mouse_drag_pointer=icon//or any icon really
//Dragging this obj on your contents tab should make the mouse icon be it's icon but if you have mouse_pointer_icon set, like above, it doesn't. The mouse icon continue to be the mouse_pointer_icon set.
//This shouldn't be the case, and it wasn't.

mob
New()
..()
var/obj/dragtest/X=new
contents+=X

Pretty much the one-liner. 100% Reproduceable.
Lummox JR resolved issue with message:
Regression (512.1488): The behavior of mouse pointers changed inappropriately, preventing drag cursors from working.
In response to Lummox JR
There are still problems happening with mouse pointers, that didn't happen before either. If you want I can make a different report.

I try to drag an obj that has an mouse_drag_pointer, but I set it to 0 on MouseDrag, but I still see the icon for a breaf moment on the game.
    MouseDrag()
if(holding)
mouse_drag_pointer = holding.icon
else
mouse_drag_pointer = 0
..()


Here is a gif showing it in action:
https://i.imgur.com/sNJOkJX.gifv
A new report would be a good idea.