I have the same problems.
It seems WP-Piwik tracking code integrates correctly into the page source, but no data is transferred to piwik.
If I integrate the Piwik “original” tracking code the data is transferred correctly.
Other way round, the collected Piwik data (with the “original” tracking code) is correctly shown in the WP-Piwik dashboard.
May anyone help? Thank you very much!
