Problem with multiple SPGridView filters

I created two visual websites that have SPGridView with filtering enabled. Both SPGridViews use an ObjectDataSource object (not the same instance, each SPGridView has its own ObjectDataSource).

Filtering works fine as long as there is only one webpage per page. But after adding the second web part, the transparent filter SPGridView only works with the first website added.

How can I fix this problem?

Thanks Panos