Block-level vertical rhythm CSS rule is broken

I was re-working the html-reset.css just before rolling 7.x-3.0 and accidentally created a broken rule.

h1, h2, h3, h4, h5, h6
p, blockquote, pre,
ul, ol, dl,
hr, table, fieldset {
  margin: 1.5em 0;
}

Note there is a missing comma after "h6". What that means is that the entire rule is ignored in some browsers. So none of the block-level elements actually get the specified margin.