Unwanted effect on mouse over for submit buttons on IE

Hello,

I noticed one behavior while styling some submit buttons.

Here is how the button looks like in normal state:

Here is how the button looks like when i press mouse down on the button:

The color change is normal, according to styles.

I am wondering why the text is going down and the background image is going up, at least in IE8. I tested in FF and the works ok...

Here is the CSS style applied to button:

input[type=submit]:hover, input.submit:hover {background-color:#1990cb;cursor:pointer;}
input[type=submit], input.submit
{background:#FF8B00 url('/media/bt_arr.png') no-repeat center right;color:#fff;height:24px;margin:0;padding:0 18px 0 6px;border:0;}