What unknown space is this? [duplicate]

Website: link

Here is the problem shown: imageshack.com/a/img909/690/AjeiLg.png

The other question was the one I posted, I posted again because I have not yet had an answer that solved the problem.

My problem only occurs in internet explorer, I highlighted the bottom div in red for viewing. When resizing the window decreasing its size, there is a space of approx. 1px in size, an unknown space. What can this be?

html:

<div class="MASTER">

<div class="MT_SEM_SOMBRAS">

<!-- ... o conteúdo do site vai aqui... -->

<div id="push">
</div>

</div>
<!--FIM MT SEM SOMBRAS-->

</div>
<!--FIM MASTER-->

Css:

Div push (the one in red):

#push {
margin-left:auto;
margin-right:auto;
width:1155px;
height:227px;
            background-color:#F00;
}

Site Container 1:

.MASTER {
    width:1169px;
    margin-left: auto;
    margin-right: auto;
    min-height: 100%;
    height: auto !important;
    height: 100%;
    margin-top: 0;
    margin-left:auto;
    margin-right:auto;
    margin-bottom:0;
    overflow:hidden;
}
/*html .MASTER {
height: 100%;  hack para IE6 que trata height como min-height   
}*/

Container 2 of the site:

.MT_SEM_SOMBRAS {
width:1155px;
margin-left:auto;
margin-right:auto;
}