I've created a simple segment as a test - Visits of Referring Domain equals "google.com". See screenshot.
When I create a new project with dimension Referring Domain and metric Visits, then apply my segment to the project, many referring domains pop up. In this case, I would expect google.com to be the only referring domain, since that's all that the segment should allow.
Can there be multiple referring domain's per visit? Where are these other referring domains bleeding in from? My impression was that there is one unique referring domain per visit, but the data seems to be saying that is not the case. When I change the Segment away from Visit to Hit, then it only shows me google.com data, but I would like to look at the whole visit.
Please let me know if this is at all indicative of poor implementation.
A single visit can have multiple referring domains. Because the definition of a visit is 30 minutes of inactivity, imagine that you search on google, visit the site, then within a few minutes you search on Bing and visit the site again. That visit would have some pages with Google and some with Bing. Thus the "visits with Google" will pull in all of those pages and you can see Bing in your report.