Margins on replaced elements are being incorrectly applied. Note that the checkbox has margin applied from its container's far left instead of being adjacent to the immediately floated element (of bgcolor indianred). Firefox does this correctly.
Firefox and Chrome both handle the checkbox case properly, Safari does not.
<rdar://problem/96980226>
It is fixed - I remember fixing it here - https://github.com/WebKit/WebKit/commit/7adc3dd2a2260a3dd133dbc2245a9be5b8b78772 *** This bug has been marked as a duplicate of bug 264770 ***