unfortunately I've found another bug which I think is somehow related to the same problem. Maybe it's already fixed with your proposed change for the 2016 SP1.
I've updated the sample project. There is a RadGridView with enabled filtering. To reproduce you have to use one of the filters which opens a filter dialog which have a RadDropDownList. So "Available filters" ... "starts with" ... and then with or without entering any filter value close or cancel the dialog.
This results in a System.InvalidOperationException "Control ... accessed from a thread other than the thread it was created on."
Form the Exception/Callstack:
bei System.Windows.Forms.TextBox.ResetAutoComplete(Boolean force)
bei System.Windows.Forms.TextBox.Dispose(Boolean disposing)
bei System.Windows.Forms.Control.Dispose(Boolean disposing)
bei Telerik.WinControls.RadControl.Dispose(Boolean disposing)
bei Telerik.WinControls.UI.RadDropDownList.Dispose(Boolean disposing)