In the file prototypes/technologies-updates.lua you redefine the unlocks for the Oil Processing research. I guess this was done to remove the Solid Fuel unlock and move it to Lithium, but this clobbers any changes made by any other mods.
I don't know if there's a simple way to remove unlocks from a tech like there is to add them. For now I've just removed the offending lines and everything is fine.
