Delete Key doesn't work in MS VS 2019 Rich Text Box

Question

Using MS VS 2019 C#

 

I have 3 RichTextBox's on my Form. Two are 64 Chars size multiline and one is 1024 size multiline.

The two 64 char boxes have all expected functionalities, the 1024 size box has all expected functionalities ... except the "Del" keyboard key does not function.  It functions in the other two but not in the 1024 size box.

 

I have scrutinized the Properties and do not see any differences except the "Size".

 

I had a similar problem with the "Enter" key which initially did not function but found that to be because I had the "Accepts Tab" set to true as I thought that I might want to use a "Tab" in the document.  Apparently, the "Accepts Tab" must be 'false' if you want to have the 'Enter' key perform a 'New Line' function.  But that did not seem to affect the "Del" key.  It works in the small Boxes but not the larger one.

 

Any recommendations ?