For example, even with Cortana and searching the Web from the Start menu disabled, opening Start and typing will send a request to http://www.bing.com to request a file called threshold.appcache which appears to contain some Cortana information, even though Cortana is disabled. The request for this file appears to contain a random machine ID that persists across reboots.

As the article notes, it appears to be harmless traffic, but it still shouldn’t happen.