Yeah, this should happen in the core if the screen type is set to LCD, and there should be some way for drivers to "opt out" as well. Sega handhelds were notoriously smeary (playing Sonic 2 on a Nomad is a real experience for that reason), but others aren't so we don't want to pin drivers that don't have the effect with it.
Either you or Haze are more than welcome to fix it. In the meantime, I'm off. The level of ingratitude for trying to slog through a few old bugs is making my head spin.