Dropdown list Auto Switch when page was in ideal

Suppose I have two dropdown lists and in first dropdown list have 5 elements and according that 5 elements second dropdown list have its different different sub elements so if I select any one from first dropdown list and then left page as an ideal mode for some time and then check that page so it will be auto change…

For example 1 Dropdown list has AA, BB, CC, DD, EE elements.
2 Dropdown list has sub elements according 1 dropdown list

if I select in 1 dropdown list as AA so according that its sub elements open but for some time I left page was in ideal mode so that 1 dropdown change into the BB but its sub elements are same as previous

so how can I replicate that issue......