On my site (AnneTannes Kruidenklets) I configured the header to show 'horizontal bar 1' just above the header image, and the page menu bar below it.
'Horizontal bar 1' is set to have a left-, top- and right border "solid 1px #AF9EB3;", and the page menu has the same border around all menu-items.
This gives me the desired effect to the left, but on the right, horizontal bar 1 is just 1px wider than the header image and the page menu bar.
I have combined a screenshot of both sides, and enlarged it to make the difference more obvious:



I've tried to add a 1px margin to the bar, but that doesn't work.
I know it is a tiny detail, but I'm rather picky on this kind of things. Someone a suggestion how to solve this?

Does it work in all browser if you set

div.horbar1 {
width: auto;
}

Thank you Flynn,
At least it works in FireFox, Epiphany and Opera. I'll have a look at I.E. tomorrow when I have access to a Windows machine...

Works for me in IE 6,7 & 8