Currently in the final stages of browser testing a new site design, and with the exception of a few remaining tweaks the current iteration looks exactly as expected in FF3-3.6, Safari 3-4, recent Chrome, and nearly perfect apart from a few CSS3 properties not supported in earlier FF, Safari, and Operas, and even IE8. Pages are relatively simple HTML5 with moderately involved CSS, though I'm not using anything fancy apart from some border-radius, box-shadow, and @font-face things in the stylesheets. So I wasn't expecting any surprises with Safari 5 today. Oops. For some reason I'm not so far seeing, Safari 5 is dropping a floated box down by a single pixel relative to the two boxes (also floated) beside it. What's odder still is that all three boxes have -1px top margins to cause them to "erase" the 1px border of the containing box, and despite the 1px downward jog the containing box's border isn't visible. It does this in both 10.5 with a Software Update installed Safari 5, and 10.6 with a downloaded WebKit nightly from today. I'm still trying to prune down to a testcase, but does anybody have any off-the-top-of-your-head suggestions as to what might be causing this? Sample page with the issue: http://tinderbox.animeworld.com/reviews/windnamedamnesia.html The issue is on the "See Also" section of the three-column box with blue headers; they should be flush across the top, and will be in any other recent-vintage browser. The page validates as HTML5, as does the stylesheet, excepting the -moz and -webkit bits. Here's the un-compressed stylesheet. What's disconcerting is that IE7 has a VERY similar looking issue on exactly the same box. In its case, of course, it's caused by the fact that, even in a very minimal testcase, if there's a div to the left of a left-floated div in the same containing element, and the floated div has a negative top-margin, it cuts off the top of the div entirely. This obviously isn't anything to do with the same bug, it's just that after spending a half-hour pruning down an IE7 testcase on that bug it's nasty deja vu to see something similar pop up in my browser of choice.