Borders appearing even when border is set as 0

Hi! I have noticed that in the last two emails I sent that I built in the newest email editor, the messages show up as having outer borders around the content when I have sent them, even though no borders appear either in the editor itself or with the "Preview" function. Under the "Design" tab the "Outer border" is definitely set as 0, which I thought should make it invisible, but it appears anyway. This seems to be a bug and I wanted to report it and describe it here to see if anyone else was experiencing it.