Role icon transparency lost when using custom emojis

When setting the icon for a role to a custom emoji from that server it shows the icon with transparency.
Once you hit 'save changes' the transparency is replaced by black.
(This does not happen for default emojis.)
Not sure since when this has changed because it worked fine a few weeks ago.

Uploading the image instead of using the emoji can be used as a workaround btw.