I'm not sure, I haven't studied the new code in details (too many changes throughout the entire firmware these past few months), but I don't think much has changed there - it's mostly an ARP broadcast, and then any answering MAC gets probed to determine its OS, services, etc...
It's possible that even in sleep mode, the printer is visible by networkmap, and the new probing causes it to wake up (could be a test checking to see if it's offering printing services perhaps)?
This is just a guess however. If the wakings happen often enough, you could try killing the networkmap service on the router, and see what happens over the next hours. That won't make the issue any easier to fix, but at least you'll know for sure.
Over ssh:
And avoid accessing the router's webui during that time (in case you hit one of the pages that causes the service to restart itself).