Okay, this release is much cleaner, more stable, etc. I corrected the performance problems simply by using an Observable collection instead of doing myListBox.Items.Add. This allowed me to rip out all the code that I had written to manually swap rows in and out with a fixed-height listbox. (When you start writing over-complicated code, you sense it. I am back in the elegant sweet spot zone again.) I removed the dependency on C5 as this is no longer used.