Undoing changes to words wrapped in annotation ranges throw InvalidCastExceptions as AnnotationRangeStarts are casted to AnnotationRangeEnd. Steps to reproduce: 1. Add a bookmark to a word 2. Add a bookmark to the following word in the document 3. Use the find dialog to highlight those two words 4. Bold the text 5. Press Ctrl+Z to undo Observed: Repeated InvalidCastException dialogs Fix available in LIB Version 2018.1.430.