Eval to fifo can be canceled by SIGINT in bash, but not in dash

EDIT: probably a bug, reported as https://github.com/mawww/kakoune/issues/3751

Run kak like below and press Control+C. When using bash this cancels
the background command, while with dash or zsh it seems to run for the full 5 seconds.
What could be the reason for this?

# repro.kak
nop %sh{
  rm -f /tmp/fifo
  mkfifo /tmp/fifo
    eval 'sleep 5' >/tmp/fifo 2>&1 &
  ) >/dev/null 2>&1 </dev/null
edit -fifo /tmp/fifo *my-fifo*
# Interrupt works with bash:
KAKOUNE_POSIX_SHELL=/bin/bash kak -n -e 'source repro.kak'
# Interrupt does not work with dash:
KAKOUNE_POSIX_SHELL=/bin/dash kak -n -e 'source repro.kak'