emacs' makefile-gmake-mode, loaded automatically for makefiles, also hides this. I've set indent-tabs-mode to nil in my .emacs for years, but the mode knows it'

emacs' makefile-gmake-mode, loaded automatically for makefiles, also hides this. I've set indent-tabs-mode to nil in my .emacs for years, but the mode knows it's needed, and will indent the line with a highlighted tab ( until you begin writing in the command to follow it, when it unhighlights it ).