Can confirm the bug with the error message "KDEInit kann /usr/bin/apper nicht starten" (KDEInit can not start /usr/bin/apper). This happens for me since I upgraded to stretch.
Tests: - start apper from the KDE menu and press the close button. <OK> - start apper from Konsole terminal and press the close button. <OK>. - create a link to apper on the desktop and click on it. Then press the close button. Error message "KDEInit kann /usr/bin/apper nicht starten" (KDEInit can not start /usr/bin/apper) is shown, <Not OK> -open dolphin, go to Desktop folder and click on file org.kde.apper.desktop. If it asked if it should be executed select execute. Error message "KDEInit kann /usr/bin/apper nicht starten" (KDEInit can not start /usr/bin/apper) is shown <Not OK> -create a quicklauncher and start apper from it. Then press the close button. Error message "KDEInit kann /usr/bin/apper nicht starten" (KDEInit can not start /usr/bin/apper) is shown <Not OK> Seems to be related to the .desktop file.
