You can encode the background images to avoid this issue if using a sprite is not possible. See Fiddle...
button {
height: 44px;
width: 106px;
background-image: url([data:image/png;base64,...]);
background-repeat: no-repeat;
border: none;
outline: none;
}
button:hover {
background-image: url([data:image/png;base64,...]);
background-repeat: no-repeat;
}