Board Thread:New on Terraria Wiki/@comment-24129632-20131104085129/@comment-1466854-20131104223540

Not a bug per se, more of a bad bit of luck in world generation. It's not supposed to happen, but the nature of random generation makes strange things happen sometimes. You can also get jungle temples with no altar in them, making it impossible to summon the boss there without carting one in from another world (requires picksaw to pick one up). It's frustrating, and this is the first time I've seen one isolated, but it happens. Personally if it's in a world you like and want to keep working on, I'd make a secondary world, wipe the temple in it, get your picksaw, and use it to "repair" this one.