I did try your suggested method again, but I'm still seeing the same results, which is my new combo box hasn't been added.
The code snippet below is called during the EditorCreated event. I get the StackPanel of the FilterMember combo box, create a new RadComboBox and Insert it in the StackPanel at position 0. What I expect to see in the UI, is a StackPanel (orientation horizontal) which contains the new comboBox I created that is blank, the member filter combo box, the operator combo box, and the filter editor.
Based on my code snippet, is what I've stated above correct, because I only see the regular telerik panel.
When I place a break point at the end of my code snippet, I see that stack panel has an additional control, which leads me to believe I've added it correctly. However it doesn't show up; and with each additional filter that is added, the count increases by 1 (not a total of 6 controls in the panel), but 6 controls, then 7 controls, then 8 controls; etc.
var telerikMemberCombo = dataFilter
.FirstOrDefault(rcb => rcb.Name ==
var memberComboParent = telerikMemberCombo.Parent
var rcbCustomRecords =
Thickness(0, 0, 8, 1),
HorizontalAlignment = HorizontalAlignment.Stretch,
Height = 25,
Width = 25