Just found a bug that lets you become invincible, even to the admin kill command. This was found by accident and is actually a bit of a problem for me :biggrin.gif: Unfortunately, once invincible, you can no longer pick up items, but you can still dig.
What happened was I lagged while logging in to my server, I was far away were I was scouting and decided to go back to the spawn point by the most obvious method....hop in the ocean and drown. The segment I was in finished loading after I was already underwater and out of air....but my health never started going down. After realizing this, i attempted jumping off a cliff, playing creeper tag, and taking a lava bath, all of which were unsuccessful. I tried digging and it actually worked, i could dig anywhere, even make underwater tunnels. Logging out and back in doesn't help either, the effect seems to be permanent (and I can't kill and reset myself with the admin command either O_x)
Just kinda a FYI to other SMP players....always wait at least one minute after loading to swim!
I have had this happen to me several times as well. The only way to solve it is to wipe your character data from the server.
The easiest way I have had this reproduced is by killing yourself on two things at once. It most often happened when a creeper followed me off a cliff when I had low hp and he exploded with me on the way down as I went splat.
You are also invisible to everyone else on the server while you are like this, but mobs still know you exist. So you can do fun things like get a train of 10 creepers following you(they won't explode because they can't see you even though they sense you and will follow you.) Run to a nearby friend, listen to them freak out over vent as 10 creepers suddenly drop out of the ceiling onto them.
This "can" also be technically a dupe problem as well, as when you "die" producing this you drop all your loot. However you still have all your items in your inventory, and you can drop them allowing someone else to pick them up a second time.