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If there is a stack of neutral, gray-colored monsters on the map, you can do whatever you want with it, no problems... However, if the monsters are NOT gray-colored, there is a chance that one of the stacks will be gray-colored. This stack disappears if you attack these neutrals and run away without doing anything... This is a bug, and the ban only applies to this specific situation.
Thank you, Amber Soler, that's exactly what I was interested in....