bash trap ignore signal - race condition

[Roman Rakus]

There's a race condition when you can hit following:
      set_signal_handler (sig, SIG_IGN);
      change_signal (sig, savestring (string));
      set_signal_handler (sig, trap_handler);
in trap.c file, set_signal() function.
So bash set signal to be ignored and then set it to be handled by 
trap_handler. However how should bash behave when the signal is received 
when the trap_handler has been set before. Check the following reproducer:

#!/bin/bash

cat>  traploop.sh<<EOF
while true; do
    trap exit SIGUSR1;
done
EOF

chmod a+x traploop.sh

i=0
while true; do
    ./traploop.sh&
    sleep 1
    echo "Sending SIGUSR1 to $!"
    kill -SIGUSR1 $!
    wait $!
    echo "No. $i: OK"
    i=$((i+1))
done


You can send SIGUSR1 to bash running traploop.sh in the state, when the 
signal is ignored, but shouldn't be. Is there any reason why is the 
signal for short time ignored?

RR