Unfortunately, many payment systems represent the dropdown for the months with zero-padding while others are without.
Usually, typing the 0 (because it's on the card) will – if it's not included in the dropdown – not select the correct month. This can cause frustration for the end user. The best way to input credit card information, would be to only have text-fields.
agreed but on mobile I find spinning through the drop-down more annoying than typing the exp date.
(Sometimes it's weird with a list of states, where it might be sorted by the state abbreviation while showing the state name or vice versa.)