Hi Jan,
Sorry for the inconvenience caused.
We encounter the crash issue when bound the GroupBar using ItemsSource and we have logged the defect report internally. We would be working on this, If you interested in getting a patch for this issue, then you may create a Direct-Trac incident under the following link.
http://www.syncfusion.com/Account/Logon ReturnUrl=%2fsupport%2fdirecttrac
Please let us know if you have any queries.
Regards,
Sakthi