Breaks Nework Connections on Raspberry Pi (Raspbian stretch)

[DragonflyNet67]

As soon as the command scheme.save() is issued the file /etc/network/interfaces is overwritten and after a reboot no connection is available anymore. No etc0 nor wlan0. The file interfaces should have the following content in order to work:

# interfaces(5) file used by ifup(8) and ifdown(8)
# Please note that this file is written to be used with dhcpcd
# For static IP, consult /etc/dhcpcd.conf and 'man dhcpcd.conf'
# Include files from /etc/network/interfaces.d:
source-directory /etc/network/interfaces.d