In certain versions of Webkit a comma is automatically added to input fields with the HTML5 attribute
type="number". In most situations a thousands separator is a nice visual device, but it’s not really applicable to numbers like ZIP codes. In the meantime, there is a workaround until the webkit team addresses the bigger issue.
Personally, this one might be worth waiting out. I’m not sure which option I like least, unintended formatting or using the
type="text" attribute for a number field.