According to section 10.6.3, auto vertical margins of block-level elements in the normal flow should become zero. This does not happen (see test case above). You seem to be using auto for vertical margins in ua.css for things that you want to have nonzero vertical margins, so that those margins can then be computed in the browser. These margins should be given in em in ua.css so that auto can be treated properly. The first-child problem could be solved by implementing the CSS2 selector :first-child. (and then that kludge (bug 1580?) could be removed...)

Actually, :first-child won't work because of anonymous boxes.

Setting all current Open/Normal to M4.

This appears to have fixed itself as of build 1999-03-09. See also bugs #3542 and #1583.

Using 3/11 build, verified fixed. Margin-top and margin-bottom values set to 'auto' compute a value of 0.