sieve script not modifying header

[Marc]

From the command line the sieve script is modifying the header like this:

su testuser -s '/bin/bash' -c 'cat test.msg | /usr/lib64/dovecot/sieve-execute/sieve-test'

However when executing via dovecot, the header stays unchanged

require ["copy","fileinto","vacation","vnd.dovecot.execute","editheader"];
# rule:[testing2]
if not execute :pipe "sieve-test" {
}

Any idea what I am forgetting to configure/allow?