[PROBLEM] Top menu in Opera

[p4trykx]

There seems to be a problem with expanded menu item. The background becomes transparent.
I think it's because the bacgorund-image in stylesheet is set to non existing gif. It seems to work in other browsers but somehow Opera treats it different.

Code:

<li class="menu-item menu-item-type-post_type menu-item-object-page menu-item-81 sf-ul sfHover">ev
<a href="#" class="sf-with-ul" style="position: relative;">ev
<ul class="sub-menu" style="background-image: url("http://xbian.org/2012/12/xbian-1-0-alpha-4-out-now/x.gif"); visibility: visible; display: block;">
<li class="menu-item menu-item-type-post_type menu-item-object-page menu-item-507 sfHover" style="background-image: url("http://xbian.org/2012/12/xbian-1-0-alpha-4-out-now/x.gif");">
<a href="http://xbian.org/getting-started/" style="background-image: url("http://xbian.org/2012/12/xbian-1-0-alpha-4-out-now/x.gif"); position: relative;">ev
</li>
<li class="menu-item menu-item-type-custom menu-item-object-custom menu-item-588" style="background-image: url("http://xbian.org/2012/12/xbian-1-0-alpha-4-out-now/x.gif");">
<li class="menu-item menu-item-type-post_type menu-item-object-page menu-item-506" style="background-image: url("http://xbian.org/2012/12/xbian-1-0-alpha-4-out-now/x.gif");">
<li class="menu-item menu-item-type-post_type menu-item-object-page menu-item-505" style="background-image: url("http://xbian.org/2012/12/xbian-1-0-alpha-4-out-now/x.gif");">
</ul>
</li>