LDAP servers are expected to be there, thats why there is also a failover server which can take over. Agree that the maintenance mode makes a lot of sense if you can’t assure reliable LDAP presence.
In 10.0 = ownCloud X we are making this more reliable with the user table and soon also a group table which will mean less LDAP calls and higher reliability when we can’t reach it. But basically if LDAP is not present its a non-defined state. There are also some background jobs around groups which could start running at this time and those would make things worse. Are your shares with groups from LDAP in any case?