Can't edit Message field when setting up a "send mail" function

Can't edit Message field when setting up a "send mail" function

Setting up a "send mail" function on a form, I click Edit to edit the From, To, Subject, and Message. I can edit the first 3 fields fine, but cannot edit the Message field. Clicking on the text box does not show the "xxx Mode" tabs and does not allow changing of the text. This happens to be for the Form Action "On Edit" | "On Success".
 
I did just now try the Free Flowing Script option, and that does allow me to change the script, so that is a work-around. So this problem is just in the Script Builder.
 
Thanks!