Optimize CSS causes incorrect #header-region ul.nice-menu ul, top:

no caching:

ul.nice-menu ul, #header-region ul.nice-menu ul {
border-color:#CCCCCC -moz-use-text-color -moz-use-text-color;
border-style:solid none none;
border-width:1px 0 0;
left:-1px;
margin-right:0;
top:1.7em;
}

caching:
ul.nice-menu ul, #header-region ul.nice-menu ul {
border-color:#CCCCCC -moz-use-text-color -moz-use-text-color;
border-style:solid none none;
border-width:1px 0 0;
left:-1px;
margin-right:0;
top:1.8em;
}
css_bd...42d.css (line 139)

when I look in the nice_menus_default.css I see there have been attempts to fix this that haven't worked:
ul.nice-menu ul,
/* Repeat for Garland header. */
#header-region ul.nice-menu ul {
top: 1.8em;
left: -1px;
border: 0;
border-top: 1px solid #ccc;
margin-right: 0;
}

/* Override for Garland header. */
#header-region ul.nice-menu ul {
top: 1.7em;
}

If I put the latter css into mysite.css zen subtheme it still doesn't work with caching turned on. Caching seems to want to take the former 1.8em, rather than fixed 1.7em;