Hi,
All skins are missing two declarations:

.imgSectionHeaderTitleDisabledclosed
.imgSectionHeaderTitleDisabledopened

Disabled section stack use them. I use sections in some of my forms and when I disable them, sections headers look weird. So I just added this style to css.

Code:
.imgSectionHeaderTitleDisabledopened,
.imgSectionHeaderTitleDisabledclosed {
    font-family:Verdana,sans-serif; font-size:11px; font-weight:bold;
    color:grey;
    border-left:5px;
}
Maybe you could add this to the next release.
Best regards