I doubt it was a magic number, but just an emergent property of how quickly the system could track a certain number of targets. When they saw problems in testin

I doubt it was a magic number, but just an emergent property of how quickly the system could track a certain number of targets. When they saw problems in testing, a workaround was devised, and the 150 number probably came from just counting the number of targets when things started to go haywire. Most likely a bug report was put in the queue, and it never got prioritized because new complaints stopped coming in.