The service stash file should contain:
cn=kdc-srv,cn=krbContainer,dc=example,dc=local#{HEX}...
cn=adm-srv,cn=krbContainer,dc=example,dc=local#{HEX}...
where the "..."s are the hex encoding of the supplied passwords. In what way is the file malformed? libkdb5_util is able to read a password from it, or you would see an error about reading the stash file instead of an error about the LDAP server rejecting the credentials. If I run the given commands, the resulting file does not seem amiss.