Setting an Enderman on fire with flint and steel, or lava, will not make it teleport away like it does when it walks in to water. Allowing players to just pour lava on their feet and wait for them to drop their loot.
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I disagree. This, at least the lava part of it, is most certainly unintentional. It's not that there's an error preventing it from working that way, it's just they forgot to make it work that way. Endermen are smart enough to teleport away from sources of damage; the most dangerous substance in the game should be no exception.
Of course, flint and steel makes sense, because you don't stop being on fire when you teleport away from what set you on fire.
If it were fixed, it WOULD break a few mob traps, but the smart ones were using piston traps anyway, which would still work.
This is intentional behavior
http://www.minecraftwiki.net/wiki/Enderman#Teleportation