textbox ghost

This is from a userform that has worked for nearly 2 years over various versions, there are 3 textboxes and numerous other controls, but as of yesterday, the textboxes have developed a ghost border covering other items. Each time I open the form the ghost can jump from one textbox to another but is always surrounding at least two of the textboxes. I even tried opening an older version and it has the same issue, so it isn't connected to a single file. Does anyone have an idea what might be causing this.