If sh receives a SIGINT signal in command mode (whether generated by typing the interrupt character or by other means), it shall terminate command line editing on the current command line, reissue the prompt on the next line of the terminal, and reset the command history (see fc) so that the most recently executed command is the previous command (that is, the command that was being edited when it was interrupted is not re-entered into the history).
If sh receives a SIGINT signal in insert mode (whether generated by typing the interrupt character or by other means), it shall terminate command line editing with the same effects as described for interrupting command mode; ...
POSIX 2013 requires SIGINT to interrupt line-editing. Yash 2.41 is just ignoring SIGINT.
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/sh.html#tag_20_117_13_03
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/sh.html#tag_20_117_13_04
cf. http://austingroupbugs.net/view.php?id=347