OK. I noticed that too, as well as the fact that the example map didn't quite work for me.
The key to a successful level_change is perfection. Take a hallway with a map change in the middle. The best way to do this is to first create the hallway in a seperate map. Place an info_landmark in it. Copy this hallway into the maps that you want the change to be in. Now place your trigger_changelevel's in the correct positions. Make sure you setup the options correctly. Now compile the first map but don't go through the the change. Compile the second map (place the info_player_start away from the change) and don't go through the change. Open up Half-Life and load the first map. Now go through the level change. It should work perfectly!