Wrong offset

[imgen]

When I use RequestReduce, one of the image's background-position is -1405px 26px which actually should be -1405px 0px, why this? The thing is I can see that all the images are combined horizontally, so where does this mysterious vertical offset come from?

[imgen]

Our CSS is

.epcHeader {
    width: 1024px;
    min-height: 110px;
    background:url("../Images/header_background.PNG") repeat-x scroll 0px 26px transparent;
    padding: 0px 0px 0px 0px;
    font-size: 13px;
}
.epcHeader .heading {
     margin: 0px 50px 0px;
     font-weight: normal;
     overflow: hidden;
}

.epcHeader .logo{
    background-repeat: no-repeat;
    background-image: url('../Images/expedia_partnercentral.png');
    margin: 0px 15px 0px 0px;
    float: left;
    display: inline-block;
    width: 194px;
    height: 38px;
}

I guess the .epcHeader class is where the 26px offset comes from. But how do we fix this?