Reproduction steps (tested w/ emacs -Q):
   Version: GNU Emacs 26.2 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.8) of 2019-04-13

   1. M-x org-mode
   2. (insert "* ")
   3. M-x org-set-tags-command, enter any tag name
   4. M-x org-todo

   The tag jumps right next to the asterisk (expected: stays where it is). Doesn't happen if the title is not empty.

   5. M-x org-set-tags-command resets the tags back where they belong

   I think it's a bug.