This only happens for me in Safari (OSX 10.7.3). If I am on Milepoint and then navigate to another tab, and then return to the MP tab (after some time period), a majority of the tab turns black. As soon as I scroll, all is well. Only happens for me in Safari. Weird, huh?
Upon further review p), this appears to be a bug in Safari 5.1.x. Not all sites are impacted, but Milepoint appears to be one that is. Unfortunately, at this time the best recommendation we can offer is to upgrade to the latest version of Safari - 5.1.7 - and see if Apple has resolved the issue in that version. Others around the net are also reporting the bug via the "Report Bugs to Apple" link under the Safari menu item. If enough reports are sent perhaps Apple will patch it.