This is a gnulib bug and should be been fixed by:
1. https://git.savannah.gnu.org/cgit/gnulib.git/commit/?id=aae308a3354bb3d0ae0bdf8647ce9be8e46abbce
2. https://git.savannah.gnu.org/cgit/gnulib.git/commit/?id=6ee6c7189f4bafbb603ef043fdf44b84c3f7532a

sed 4.9 is the first release to have these changes.