The red dotted selection box surrounds the current selected item when designing your menu in the visual interface. This box is not part of the menu, it simply helps identify which item is currently selected during visual design.

You can temporarily hide the box by clicking anywhere within the document, expect for the visual tool interface and menu. The selection box may automatically disable itself when using certain add-on's such as the follow pointers.

To permenantly disable the box while designing a menu, click settings --> options from the main menu and choose the 'Hide Selected Item Box' option.

During preview the selected item box will be hidden from view for a 100% accurate representation of your menu.