Bukkit/CraftBukkit — comment on commit 5b36c2f96ca0a7a4d151ece412a9ff33cff6fd36
File: src/main/java/net/minecraft/server/EntityHuman.java line 843
By EdGruberman:

I believe you forgot to actually call this event as occuring. Perhaps something like:
Bukkit.getPluginManager().callEvent(combustEvent);