Absolute site links are converted to relative links when clicking the HTML button in the editor. Links are converted whenever you click the HTML button whether you make changes or not. We've seen this problem in Safari, Chrome and Firefox but not all the time. We only have problems with the link conversion when we open the HTML edit window and the Update and Cancel buttons are reversed and in color, i.e. the Update button is green and on the left and the Cancel button is red and on the right. When the buttons are grey, with the Update button on the right, the absolute links are not converted. We have encountered the problem on different machines running the same version of the same browser and the same version of WordPress.