Easy to reproduce by installing libldap-2.4-2:amd64, removing (but not purging) it, and then trying to install :i386.
Klaus: in this case a workaround is probably to purge the old packages (apt-get purge libldap-2.4-2:amd64 libldap-2.4-2:i386) before trying to install them again.
Thanks for the report. I guess this is caused by https:/ /bugs.debian. org/330695 which is not fixed yet. :/
Easy to reproduce by installing libldap- 2.4-2:amd64, removing (but not purging) it, and then trying to install :i386.
Klaus: in this case a workaround is probably to purge the old packages (apt-get purge libldap-2.4-2:amd64 libldap-2.4-2:i386) before trying to install them again.