You get not dates, but datestring texts. The reason is, that the date format in your windows regional settings is different from format used in web page (in web page the format is "dd/mm/yyyy" - I don't know is it US or UK format, but it is sure in your computer it must be different. E.g. for me the short date format is "dd.mm.yyyy", and I see the 1st date in column A (the date you obviously reentered) in this format. All other dates are for me strings.

I could easily convert all those strings to dates - I selected the column A, and replaced all "/" with "." (i.e. with my date delimiter).