This is an issue relating to using the damage effect command (/effect 7) on a player on multiplayer. For this to glitch, damage level must be greater than 14.

What I expected to happen was:
Recieving the effect would kill the player.

What happened was:
Death message appears ("was killed by magic"), but the Player is not killed. No death screen. Player is unable to activate switches or recieve any other damage (such as from falling). Placing blocks and destroying blocks seems possible but there is no break sound and no drop. Chat window opens but typing text and hitting enter does not publish text. Switching to gamemode (via /gamemode 1) not possible. Logging out of server and reentering causes the death screen to immediantly pop up. After respawn player has gamemode 1. Blocks previously placed are gone (back in the players inventory).

Steps to reproduce:

• Log in onto a server.
• Place down a Command Block and type in /effect @p 7 1 15 (damage effect for 1 second at level 15)
• go into /gamemode 0
• activate Command Block (will show '@: Given HARM (ID 7) * 15 to PLAYER for 1 seconds' and 'was killed by magic' but no death screen)

Not tested while other players were on the server. When on singleplayer, this issue does not occur, tested with damage lvl 20 and was killed as planned.

This will probably fall into the category 'weird things that happen with too large effect levels'. I still thought this would be somewhat important. If not, mark with works as intended or something like that. Applies to 1.5.2 as well.

Through PVP with high strenght level:
When a player kills another player and the killer has a too high strength level (for example 114 or 115), the player that got killed sees his death message, but he only gets half a heart of damage apparently, but after that he loses server sincronization until he receives the death (it takes a long long time), if that player (the one who died) disconnects and connects again (relogs), then it shows he died.