Image Upside on 1st page load

On my website, the first time anyone loads this website, the rounded corner to the right of the main navigation is upside down. The image in question. When you refresh the first time, the image flips to the correct position.

I have checked in the folder where the image is kept and it IS the correct version. The website's cache has been cleared and still this bad image insists on appearing the first time! Any help? The is the CSS positioning the image:

/* Top right rounded corner */
.primary_nav_right_corner {
	width:14px;
	float:right;
}