This is a quick follow-up to inform you that the Support ticket you have sent us has been handled.
In short, the issue was caused by type mismatch between the View Model property definition and the property defined by RadJumpList.
RadJumpList exposes the GroupDescriptorsSource property which is IEnumerable<DataDescriptor>, whereas your View Model exposes a property of type ObservableCollection<GenericGroupDescriptor>. The issue here is related to the difference between the GenericGroupDescriptor and DataDescriptor usage for the generic definition. ObservableCollection is IEnumerable which is OK, but since Generics are not inheritable, DataDescriptor is considered different from GenericGroupDescriptor, although the latter inherits from DataDescriptor.
I hope this helps.
the Telerik team
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