2 tracked Blogs: Report 1 shows both(!), Report 2 2nd blog only


Strange behavior with the dashboard:

1.) I started with 2 blogs in a WPMU (WP3) installation. I addded one tracking code into the footer of the template, which is the same for both. Of course I get one Dashboard with both blogs results summed up.

2.) I found out that putting the tracking code in WP Widgets helps me to differentiate between two blogs with still the same template. So I removed the tracking code from the footer of template and created a new tracking ID for my 2nd blog.
I added tracking code (with ID=1) to the first blog into a txt/html widget.
I added the new tracking code (with ID=3) to my second blog.

The dashboard for blog 1 still shows hits from both blogs, which is wrong. The dashboard for blog 2 shows blog 2 only, which is correct.

I made sure, the source code of each pages only contains the correct tracking code. How can it happen Piwik still counts blog 2 results under ID=1?