Issue with div's background image in Opera

Hello,

my name is Roman. I've a bit issue, that I can't resolve by myself.

In html document I've a "div" with id "menu". The css class "menu1" is assigned to this div (via class="menu1"). And I need this class to be changed after clicking on the div. I've wrote javascript function with code like this:

document.getElementById('menu').className = "menu2";

and assigned the function to div's "onclick" action.

Menu1 and Menu2 has different background images described on css file. So all works well in Chrome, FireFox and even in IE, but not in Opera browser. Opera doesn't update the new background image after clicking and updates it only after some other mouse action, for example minimize and maximize the browser window.

Can some of you help me?

Thanks,

Roman.