TOC Binding Error after Editing Renderer and Refreshing Legends

[GeoITwinkle]

I recently implemented some user controls to support editing feature layer's renderer. The legends in TOC refresh correctly, but it always throw binding error. Below is the code to simulate the editing and refreshing process, and attached is a testing project. It does not have obvious side-effects so far, but I think it may worth looking into. Thanks!

WpfApp1.zip