This appears to be a richedit control issue. If there is a blank line at bottom of the text, it does not allow you to scroll down to it unless you use the arrow keys. As the editbox scrollbar and display are managed by the richedit control, there is no way to prevent that.
The reason there is a blank line at the end of the text is that lines are separated by CRLFs. So one solution might be to remove the CRLF from the last line to prevent a blank line appearing at the end. However that means in order to add new text to the end, users would have to scroll to the last line and press return. I prefer having a blank line at the end, so I would rather leave it as it is.
