WordPress Alters All Affiliate Links (Worry?)

I notice when you add amazon affiliate links say as a hyperlink via their hyperlink button in visual editor (also checking open in new window). When I go into the html, the link is slightly altered from what I originally entered. Upon using it on amazon link checker it will fail.

Is wordpress screwing up the links or is this okay as long as your tag=(id) is intact at the end of each url?