Replace dialog doesn't get focus and can't be closed

[han]

In my application intended for both Windows en Linux, I have a Linux problem. If I execute the replacedialog in the second form, form2 then after executing the replace dialog, all typing ends up in the memo and I can't close the replacedialog. This doesn't happen in the main form called "form1" It doesn't happen in Windows compiler.  I also can't close the dialog form.  The same happens with a find dialog.

Any idea what goes wrong? 

Attached a simple test program. Open the second form with the button. Then try to use the replace dialog. It doesn't work and typing ends up in the memo if it has the focus. Strangely it doesn't happen in the first (main) form with same code.

Lazarus 1.6, FPC 3.0.0