Well, it works like that:
Example:
AI with two targets
target 1: sleep node - target 2: normal path node with idle_spawnarg
If you alert the AI just a little bit, the AI will go up from sleep, look around and will go back to sleep.
If you alert the AI by showing yourself, then AI will go to target 2 and will never go back to target 1 (the sleep node). I think the logic behind this hard coded behaviour was, that you would not expect someone to go back to sleep once he has seen an enemy.