Spark Smart Modem WiFi - hidden network?

Hi

I have recently got a new Spark Smartmodem and speed etc seems good. One of the unusual behaviours is that the modem with only the 2.4/5 channels set to active a hidden network on identical MAC address (except first/last pair) shows for 2.4/5 channels (lower security protocols). On setting up the guest network it then appears (same MAC style) but the hidden network remains 'active'. I have not seen this behaviour before and it seems odd?

Any comments/experience welcome.

Thanks