Unknown escape sequence in tails-gdm-failed-to-start.service

The journal of a booted 4.0~rc1 image contains this message:

/lib/systemd/system/tails-gdm-failed-to-start.service:11: Ignoring
unknown escape sequences: "MAX_LENGTH=254 ;       PREFIX="Error starting
GDM with your graphics card: " ;       SUFFIX=". Please take note of
this error and visit https://tails.boum.org/gdm for troubleshooting." ;
      MAX_VIDEO_CARD_LENGTH=$(($MAX_LENGTH - $(echo -n "$PREFIX$SUFFIX"
| wc -c))) ;       VIDEO_CARD=$(lspci -d::0300 -nn | sed -E "s,.* VGA
compatible controller \[0300\]: *,," | cut -c
"1-$MAX_VIDEO_CARD_LENGTH") ;       /bin/plymouth display-message
--text="$PREFIX$VIDEO_CARD$SUFFIX"      "

Original created by @segfault on 17166 (Redmine)