Modal "jumping" problem

Heya guys,
I have a problem with modals.

If we have a modal window with a content longer than the height of the modal window, if I click on a select box which is below the height of the screen, the focus will jump up and the opened panel with options will fly up with it.

Do you have a fix for this irritating problem please?

It’s not really clear what happens, could you explain better? Screenshots might help.
How do you click something that is below the height of the screen? It’s not visible then?