Hi Stephan,
Thanks for your interest in Syncfusion products.
The reported issue with filtering feature has been confirmed as a defect. So please create a DT incident for this query so that we can update you with the patch once the issue is fixed.
You can create the DT incident from the following link.
http://www.syncfusion.com/account/dashboardIn the interests of maintaining confidentiality, we have a policy of not sharing patches or otherwise proprietary customer specific information in the public Forum.
Please let us know if you have any queries.
Regards,
Krishnaraj D