Problem with itemSelectedCallback scroll list

[apll]

I use a scroll list dinamic.

When i set itemSelectedCallback the itemIndex don't reach maximun element.

For example:

sl_select.setNumberOfItems(4);
sl_select.setWindowSize(4);

where max number of object can be 4, param of itemSelectedCallback pass only 0 for itemIndex.

Other example is:

sl_select.setNumberOfItems(13);
sl_select.setWindowSize(5);

where max number of object can be 13, max param of itemSelectedCallback pass is 9 for itemIndex.

What do it wrong?