Images that dissapear for some milliseconds and appear while hovering (or delay in loading hover image)?

Question

In my web site, there's two buttons in both sides of the jQuery slider. When I hover them the image disappears and then the hover image appears. (is not long, just a few milliseconds).

Do I have to preload the hover image to solve this? How to do that?

CSS:

#prevBtn {
    left: 0;
}
#nextBtn {
    left: 474px;
}
#prevBtn a, #nextBtn a {
    display: block;
    width: 26px;
    height: 58px;
}
#nextBtn a {
    background: url("../images/btn_next.png") no-repeat 0 0;
}
#prevBtn a {
    background: url("../images/btn_prev.png") no-repeat 0 0;
}
#nextBtn a:hover {
    background: url("../images/btn_next_hover.png") no-repeat 0 0;
}
#prevBtn a:hover {
    background: url("../images/btn_prev_hover.png") no-repeat 0 0;
}