In previous versions of JIRA, the Activity Stream populated content using the baseurl from the incoming request. To be more specific, it would populate data using the URL that the user connected to JIRA with.

In newer versions of JIRA, 5.0+ as far as I know, the Activity Stream data is populated using the Base URL in the General Configuration. I have been advised that this is not the intended usage of of how the Activity Stream supposedly works.