If you run a screen flash that lasts more than the default duration (0.5 seconds), you'll notice that the flash starts fading out later than in the original engine. This can be noticed in the final battle with Mary in Ib. Run the player --start-party 1 --start-map-id 93 --start-position 10 20 and walk up to trigger the cutscene. The red flash lasts so long that Mary will run at you before the flash fades.
Use correct screen flash level (fixes #644)