#activitystream is not a unique id (it used in both block and page content)

If Activity Stream module output is used on pages and blocks, both wrap their output in:

on the same page. IDs should be unique within the DOM.

To duplicate this issue, place the Activity Stream block in a region on your page. Then go to a page that outputs stream information such as:
DRUPALDIR/stream
DRUPALDIR/user/* (where * is a uid for a user with an activitystream)

Search the source for: id="activitystream" and there will be two instances.

Perhaps the block should be changed to id="activitystream-block" or something similar.