Why is bash stopping processing the script
(echo "ssh hans@mymachine.com echo hello" ; echo 'echo Done')

ssh hans@mymachine.com echo hello
echo Done

(echo "ssh hans@mymachine.com echo hello" ; echo 'echo Done') > a.sh

. ./a.sh

Warning: No xauth data; using fake authentication data for X11 forwarding.
hello
Done

(echo "ssh hans@mymachine.com echo hello" ; echo 'echo Done') | bash

Warning: No xauth data; using fake authentication data for X11 forwarding.
hello

ssh hans@mymachine.com echo hello
echo $?

Warning: No xauth data; using fake authentication data for X11 forwarding.
hello
0

trap "" ERR

( echo "(" ; echo "ssh hans@mymachine.com echo hello" ; echo 'echo Done'; echo ")" ) | bash

Warning: No xauth data; using fake authentication data for X11 forwarding.
hello
Done