Dovecot can't connect to openldap over starttls

[info at gwarband.de]

Hello guys,

actually I'm trying to configure dovecot to access openldap for 
passwordcheck.
My openldap is only allow access over "secure ldap".
The dovecot can communicate with the openldap server but there is maybe 
a failure in the sslhandshake.
Additional information you can find in the logs or in the dump below.
Also I have my ldap config from dovecot in the links below.

I have already created an bug reporting in the system of openldap but 
the answer was to get support from her.

All datalinks:
https://gwarband.de/openldap/dovecot.log
https://gwarband.de/openldap/dovecot-ldap.conf
https://gwarband.de/openldap/openldap.log
https://gwarband.de/openldap/trace.dump

The bugreportinglink from openldap:
http://www.openldap.org/its/index.cgi/Incoming?id=8615

I hope you can help me.

Regards.
Tobias Warband