Ah but Cisco refers to 5-55Mhz as the "Japanese extended upstream frequency range"

Nah you're right, I was using "extended" in reference to EuroDOCSIS being higher than standard NA DOCSIS rather than DOCSIS 3 vs. EuroDOCSIS.
Guess they must be using shiny new diplex filters. In this case the US power on 60.3Mhz is only 1dB more than 45.8.