If you are using SW2016, when you edit the sheet format, Right hand click on the sheet and select Title Block Fields. You should then be able to edit the hot spot border. Used to be Edit Title Block prior to SW 2016.
Hope that helps.
I am using 2016 but when I do as you suggest I have no "Title block Fields" come up when I right click, I am sure I used to.
I have since found out I can add a sheet format to the command Manager Tabs and after pressing it I then get a "Title block Fields" button come up I can use. So problem solved but still annoying why I cant use the way you suggested.
Minimize everything and just check to see if there are any open dialog boxes somewhere.