Just stumbled on a minor error in TWPRTFEnginePaint.PaintRTFPage/PaintLine
It can be reproduced in WPToolsDemo.exe with this rtf-document.
If you select the text "Röntgen: " including the space after the colon and then delete it with DEL or backspace, a range-check-error is thrown on line 7547
lineData.Par.CharCount is 0 and the CharPos-array is empty.
Adding an additional check for CharCount > 0 did it, so no impediment for me.
Using version 9.1.004