dovecot-pigeonhole running external script ends with signal 11

[Tobi]

Hi,

I'm running a dovecot 2.2.26 (self compiled) on a Centos 7.
I have a sieve script which should run an external script (in filter
mode) that encrypts the mail using the users pub key.

I configured 90-plugin.conf as follows

plugin {
    sieve_plugins = sieve_extprograms
    sieve_extensions = +vnd.dovecot.filter
    sieve_filter_bin_dir = /etc/dovecot/sieve-filters
    sieve_filter_exec_timeout = 10000
}

The script is named SCRIPT and is called in my sieve script

require "vnd.dovecot.filter";
if blabla {
  filter "SCRIPT" ["me at example.com"];
}

the script returns the encrypted mail.

I can call this SCRIPT without any error manually on the console as
dovecot user (vmail).
Also sieve-test "says" that the script called sucessfully

su vmail
sieve-test -e -t - -Tlevel=commands -r me at example.com -l
/home/vmail/example.com/me/.Maildir
/home/vmail/example.com/me/.dovecot.sieve /tmp/test.mail
...
23:   filter action
23:   execute program `SCRIPT'
23:   executed program successfully
23:   changed message
...
info:
msgid=<B5OEuIEvrCZzcoJ7A6fCF-ka2Nwz-Ze2UCO840Panvw.w7zr1vruaJMbDBwK63natps3v__yOgbhHy3ntACTU0s at redacted>:
stored mail into mailbox 'INBOX'.
sieve-test(vmail): Info: final result: success

and I get the encrpted message in my mailbox.

Just when it's called upon delivery via lmtp the script ends with signal 11

Jan  3 15:59:48 mbox2 dovecot: lmtp(me at example.com): Error: program
`/etc/dovecot/sieve-filters/SCRIPT' terminated abnormally, signal 11

And in ~/.dovecot.sieve.log I can find the following

.dovecot: line 23: error: filter action: failed to execute to program
`SCRIPT': refer to server log for more information. [2017-01-03 15:59:48].

I have no idea why the manual call runs perfect and the call from sieve
file ends up in this error.
Does anyone have an idea how I could narrow down the source of this
error? Or even better how to fix it? :-)

Thanks for any answer

tobi