File Open Dialogs in KDE Plasma confusing

Hello.

I am using KDE Manjaro (Plasma V5.8.2) and Mint KDE (Plasma V5.5.x).

The effect is: When IDE is in full screen mode file-open dialogs are created BEHIND the main window and therefore invisible! This is extraordinary annoying when working, especially for beginners.

This effect appears in both Versions of KDE and in both Versions arduino V1.05 and 1.6.12!

Other java aplications, like Netbeans, ganttproject.biz and MPLABX-ide are working properly.

Some ideas?

Thanks in advance.