There are a bunch of little slip ups while Deb is making the buttons. There's also a shot of her putting in a button while the STU-PID button is already in the tin, followed by a shot of her making the STU-PID button.
From memory, she has a whole bunch of 'em in a container of some sort. Is it not possible that she made multiple 'Mark Sux' buttons in different colours?
FYI Debra made many different types of buttons. Some of them said the same thing, but with different colors. Haven't you ever been to a store that sold buttons before? They sell more than one of the same types of buttons. What's the point of just selling one button? This is clearly not a slip-up at all.