Input image moves when clicked on mobile browser

Question

I have a search form on my WordPress blog, and the input image has onmouseover and onmouseout events. The positioning of those images should not change during those events. On my desktop, everything works well (the image changes, but does not move). However, on my mobile browser (Chrome, on a Samsung Galaxy S4), the input image pops out of the div and becomes an unloaded image, once you click it to perform the search.

This is the HTML:

<div class="searchform-div">
    <form method="get" class="searchform" action="<?php echo home_url(); ?>/">
        <input type="search" id="s" name="s" placeholder="Search. . .">
        <input type="image" id="searchButton" src="<?php bloginfo('template_directory'); ?>/images/searchbutton.png" onmouseover="this.src='<?php bloginfo('template_directory'); ?>/images/searchbuttonhover.png'" onmouseout="this.src='<?php bloginfo('template_directory'); ?>/images/searchbutton.png'">
    </form>
</div>

And, this is the CSS:

.searchform {
    width:   100%;
    height:  27px;
    padding: 3px 10px 0 0;
        box-shadow:        inset 2px 2px 3px 0 #7b7b7b;
        -moz-box-shadow:       inset 2px 2px 3px 0 #7b7b7b;
        -webkit-box-shadow:    inset 2px 2px 3px 0 #7b7b7b;
    background-color:      #ECECEB;
    -webkit-border-radius: 3px;
    -moz-border-radius:    3px;
    -o-border-radius:      3px;
    border-radius:         3px;
}

.searchform-div {
    width:     100%;
    height:    34px;
    margin:    10px 0 10px 0;
    max-width: 850px;
}

#s {
    margin-left:      3px;
    padding-top:      2px;
    background-color: #ECECEB;
    width:  94%;
    height: auto;
}

#s:focus {
    outline-color: #ECECEB;
}

#searchButton {
    margin-bottom: -6px;
    background-color: #ECECEB;
}

You can see exactly what I'm talking about if you go to http://www.genielauren.com/blog/ on a mobile browser, and use the search form.

I just want to know how to stop the image from popping out of the div, and why the onmouseover image doesn't load, on a mobile browser.