Diego, thanks for looking at it. i apologize for not having looked at an "emacs -Q" (and, thanks to Ihor for, a few days ago, having pointed out how to "emacs -Q" with one's "normal" org version).
: emacs -Q -L ~/.emacs.d/elpa/org-20201012/ -l org exhibits *half* of the behavior i am mentioning. ---- #+begin_src makefile a: echo foo #+end_src ---- a leading tab is converted to spaces in the Org Src buffer. but, in this vanilla configuration, when i return the source to the .org file, the spaces have been converted back into a tab. it turns out, this (in my ~/.emacs) is the culprit: : (setq-default indent-tabs-mode nil) when indent-tabs-mode is nil, the recovered contents of the source block have had the tab converted into spaces. i guess i'm at the same question: is it likely a bug, or a feature? Greg