When changing the page zoom, the CSS "width" property of some elements are off by +/- 1px. I assume this has to do with the rounding calculations when a page is zoomed. I've provided a link to a page that demos this bug. I am alerting the width of an element, and if you zoom the page in or out you can see that the width is sometimes off by one px compared to what is being set in the CSS.
I can reproduce in Safari 5.1 on Lion and Windows 7.
This still happens in Safari 15.5+.
<rdar://problem/96913055>