prevent unselect items in the listbox after right click

[masoud_sedighy]

in my list box with when i select some items (multi select:extended) and right click the mouse on that area all the items except that one there is mouse on that location , will be unselected.

i want to prevent deselecting items after right click , i would like all the items i have selected, after right click also keep selected like what we have in excel sheets.

Best Regards.