Thank you very much for explanation.
O'Reilly book "Juniper MX Series", second edition, contains an example RE filter (page 320). In filter accept-ldp term accept-ldp-unicast tcp packets to ldp port are only accepted from directly connected ip addresses (prefix-lists router-ipv4 and router-ipv4-logical-systems). However, with default config (protocols ldp transport-address absent) the LDP tcp connection is sourced from (neighbor) loopback ip. It's not accepted and as result the ldp sessions cannot be established. The list of loopbacks cannot be automatically generated with apply-path.
Is there a bug in the book (the filter is same in the first edition) or is there something I fail to understand? Most probably the latter one, please explain 
Thanks