That's weird. Could you describe in more detail what exactly happens? How long of a <WAI command are you using? I'm assuming that you're editing map number 072. Could you perhaps paste your script here?
I'm a little bit confused about your question about editing the title screen since it sounds like you're already customizing it. Do you mean customizing the main menu? If so, then part of that is just an image in the game's data filder, another part of it can be edited with Resource Hacker, and other things require assembly hacking.
That's probably happening because you have the wrong NPC spritesheet configured. Unfortunately, you can't have every NPC ever on one map, you have to place them selectively. For a dragon zombie to show up right, you need to put "Eggs2" in NPC Tileset slot 1 for your map.