Why does the checkbox stay checked when reloading the page?

<label for="showimage">Show Image</label>
<input id="showimage" name="showimage" type="checkbox" value="1" />

<label for="showimage">Show Image</label>
<input id="showimage" name="showimage" type="checkbox" />

Cache-Control: no-store

$(":checkbox").attr("autocomplete", "off");

<META HTTP-EQUIV="Pragma" CONTENT="no-cache">
<META HTTP-EQUIV="Expires" CONTENT="-1">