为什么浏览器会给我的选择元素添加额外的选项?

I'm using a date selection widget for a registration form in Django. For some reason if you submit the page with validation errors the first option element in the select is duplicated. This happens for every refresh, so if you've submitted the page 5 times, you'll have the first element repeated 6 times. Even stranger is that the widget consists of 3 selects: day, month, year and this only happens with the month select.I'm using a date selection widget for a registr