Ah yes, that's the "flamethrower starts fires" option. if you have issues with that, turn it off. It is default to false for this reason.
Honestly, I only made the option in the first place for the new spidertron named Burninator, that had a pair of flamethrowers. It sounded like it would be fun, but in practice... very not, and very buggy too. I made the option to make the flamethrower start fires like the hand-held version to see if it helped, but it didn't, so I scrapped the idea and made Tankotron instead.
Sorry for not responding earlier, I've been distracted lately.