jquery ui selectmenu scrollbar not working
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I use jquery selectmenu plugin. I have initialized select with    

    $(select').selectmenu({width:100, maxHeight:300, style: 'dropdown'});

I have many options and this causes to appear default browser scrollbar, but i cant use it. If I click and try to drag this bar, selectmenu closes. I can scroll with mouse wheel. There might be some conflict in css and various plugins. But im not sure where to start looking. 

Any ideas, what might be causing this problem?