I have a slideshow div, and I have a datepicker field above that div.
When I click in the datepicker field, the datepicker panel show behind slideshow div.
Put the following style at the 'input' text element: position: relative; z-index: 100000;.
position: relative; z-index: 100000;
The datepicker div takes the z-index from the input, but this works only if the position is relative.
Using this way you don't have to modify any javascript from jQuery UI.