While calling in a window other window at runtime all list boxes go on top

I am changing from Delphi to Linux. In a simple form I call through button in windo1. In it I want to use OpenDialog. Its icon is include in Windo1. I want to pass file information of OpenDialog to other Window2 of individual unit, which contains a pair of list boxes (to take directories and file names). Window2 contain in addition to list boxes top and bottom panel with some text and edit fields. While running program, Window1 calls Window2 and that opens OpenDialog immidiately. Then I can select directory and file an accept them. However Windo2 does not open as designed, but list boxes are collected on the top covering top panel and main part of other fields and text is missing.
How can this case solved?
Jarmo Kervinen