Even though it was single player, there was a problem with the flamer.
I was down to about 140 ammo left in my flamer, and I decided to try reloading. It worked.
I simply pressed R, and Boom! my flames are back up to 200.
This could be a problem online.
I didn't mod that version of the game in any way at all.
Hopefully, this will be fixed in 1.4.