Actually, the dircolors behavior is mentioned in the dir_colors(5) man page at the end:
FILES /etc/DIR_COLORS (Slackware, SuSE and RedHat only; ignored by GNU dircolors(1) and thus Debian.) System-wide configuration file.
~/.dir_colors (Slackware, SuSE and RedHat only; ignored by GNU dircolors(1) and thus Debian.) Per-user configuration file.
Actually, the dircolors behavior is mentioned in the dir_colors(5) man page at the end:
/etc/DIR_ COLORS
(Slackware, SuSE and RedHat only; ignored by GNU dircolors(1) and thus Debian.) System-wide configuration file.
FILES
So this is not a bug.