Float_framebuffer not being honored sometimes?

[hizzlekizzle]

In this shader preset (https://github.com/libretro/slang-shaders/blob/master/test/nonfunctional/gtu-famicom.slangp), the third pass' float_framebuffer setting doesn't seem to be honored (that is, float_framebuffer2, on the combFilter pass)

In the Cg version, changing it to false will tint the image to magenta but on the slang version, it's always magenta and toggling it true/false has no effect.