Last Thursday, Google announced how they have made a change to how they define a session.

Before Thursday Google Analytics ends a session when:

More than 30 minutes have elapsed between pageviews for a single visitor.
At the end of a day.
When a visitor closes their browser.

Now, Google Analytics ends a session when:

More than 30 minutes have elapsed between pageviews for a single visitor.
At the end of a day.
When any traffic source value for the user changes. Traffic source information includes: utm_source, utm_medium, utm_term, utm_content, utm_id, utm_campaign, and gclid.

So what impact is this having on your traffic reports in Google Analytics? It has been enough time to see the complaints in the threads.

But first, look at the comments in the post:

There are also complaints in the WebmasterWorld forums and at Sphinn.

Are you upset? Did it make significant changes to your reports?

Forum discussion at WebmasterWorld and Sphinn.

Update: There was indeed a bug. Google wrote: