I use one Google Analytics tracking code across multiple subdomains. I have created a segment for a specific subdomain (lookatme.mysite.com) and the only condition in the segment is that Hostname contains lootatme.mysite.com.
With the segment applied, I see 98 pageviews, which is much higher than I would expect. So I looked in the Behavior-->All Pages view to find out what pages people were going to. With the segment applied, I saw pages that didn't exist on that subdomain.
I then added Hostname as a secondary dimension. Keep in mind, I have a hostname condition in the segment. But in the hostname column, I see values for other subdomains.
Why do I see other hostnames when I have a segment filter on the hostname?
Example of the data I see with the segment applied:
Page Hostname Pageviews / lookatme.mysite.com 15 /page1 site1.mysite.com 12 /page2 site1.mysite.com 7 /home site7.mysite.com 4 /calendar site3.mysite.com 2