Downgrading all these packages to their previous version in Debian Testing (4.14.2-1) resulted in a working Dolphin again:
dolphin kde-baseapps-bin kde-baseapps-data kdebase-bin kdepasswd kfind konqueror konqueror-nsplugins libkcddb4 libkonq-common libkonq5-dev libkonq5-temp libkonq5abi1 libkonqsidebarplugin4a plasma-widget-folderview -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org