This is very likely related to the issues we were seeing in the UWP control when we invalidated outside of lock. It looks like this:  (the selection is above and below the prompt line)
Activity
wpf: trigger render when selection is cleared, do it under lock
wpf: fix a handful of issues with the wpf control (#6983)
wpf: fix a handful of issues with the wpf control (#6983)
wpf: fix a handful of issues with the wpf control (#6983)