Numbers automatically adds % to cells formatted as date

I have a column in a Numbers spreadsheet that I want formatted as a date: 1/1/2015 etc. But when I start typing a number in a cell, it automatically adds % at the end of whatever I type. I have already tried Format > Cell > Data Format > Date & Time. I also tried formatting the column as Text for good measure--same problem. It seems like even after I select a format for the column, when I start typing in a new cell, it defaults to "Automatic" formatting and for some reason defaults to percentage. Any suggestions?

I'm using Numbers 3.5.3.