It's always quicker to explain with a video, so I cut one together:
-Running latest Steam release of Disgaea PC
-ReShade 3.0.5 with shaders from Nov 5's git commit.
-OpenGL, 32-bit
The main menu/opening sequence is broken (and I assume more of the game is, too).
The ReShade UI only briefly flickers upon pressing Shift+F2.