[OpenGL] [next] Custom intros unleash the darkness

This is an OpenGL exclusive glitch which affects all custom intros. I've only noticed it persisting past the intro in mystic realm.

added Bug Regression Rendering OpenGL renderer labels

changed milestone to %2.2.9

Bisected the issue. It seems to be caused by !1181 (merged).

mentioned in merge request !1423 (merged)

closed via merge request !1423 (merged)

mentioned in commit c589fe85