I downloaded the launcher.exe then ran it first time and logged in. Then I changed the game directory of the first (default) profile and created another profile with the same game directory as the first. After that I pressed play for the default profile and Minecraft crashed:
Error: Couldn't find or load main class net.minecraft.client.main.Main
The Console only sad bad exit code (1). I guess Minecraft references at the first start to the wrong directory, because when you press again play, it works.