Your stylesheet as well as the page display show that you have not uncommented the display: block;
Make it like this:
Code:
.centerBoxHeadingWrapper {
    background-image: url(../images/cornbg-r.gif);
    background-position: top right;
    background-repeat: no-repeat;
    display: block;
    }
It seems that somehow .centerBoxHeadingWrapper is getting a strangely squeezed version of cornbg-l instead of cornbg-r.

And also, cornbg-r does not need to be so long - 100px or so should be enough.