This has been fixed in bash-4.4 and works as expected in rawhide.
Sorry for the wrong reproducer, because it is not obvious what I tried to
say. So just FTR:
Please don't use the '$ bash -c CMD' command, but rather real interactive
session by '$ bash'. Then hit the 'CMD' into the started interactive shell,
and try to 'ctrl^C' it. You'll see the shell is also interrupted.
Created attachment 1243822 [details]
Don't unconditionally set pipeline_pgrp to shell_pgrp
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.