it seems that having a RadPane with a binding for its IsPinned property needs to bound with Mode=TwoWay for it to work. Why is this? The problem comes more apparent when I'm using (in the real application) binding to a ViewModel that gets converted through a (Multi)ValueConverter. If I have to have the binding mode be TwoWay I have to implement the ConvertBack method of IValueConverter and have it return something like null, even though I only want the model converted one way. I absolutely do not want the pinned/unpinned status of the RadPane having any influence on my model.
Also, it seems the ConvertBack is only called once at the start of the program or when the actual pin/unpin icon is pressed. And this is very bad when we have the TextBox binding. If I write a string longer than 5 characters into it, the pane opens. If I then unpin the pane, the TextBox is cleared because the converter returns null!
Below is a repro of the problem, standard WPF .NET 4.7.2 project with only the Telerik nugets added. Clicking the checkbox Pane 1 does nothing. The checkbox Pane 2 pins/unpins Pane 2 because it is bound with Mode=TwoWay. The same can be seen with the textbox. When typing a string more than 5 characters in length, the last pane opens if the binding mode is TwoWay.
and the converter: