Actions aren't performed when disconnected
On a friend's multiplayer Minecraft server, it seems actions which I have initiated get paused when I'm not connected.
For example: if I plant a tree and come back and hour later, the tree will still be a sapling. Also, if I start smelting something in a furnace, it restores to where it was when I log back in after logging out.
Does anyone know why this is? The server's still running, so I don't see why it would be like this.
The effects you describe will only occur while a chunk is loaded. If nobody is around to cause the chunks to be loaded, these things won't progress.