ownCloud shares are removed temporarily when LDAP server is not available

Today I needed to reboot my LDAP server. The reboot caused the LDAP connection to be broken, but what made matters worse is that shares created by LDAP users are removed for non-LDAP enabled accounts.

Consider this setup:

1. User A is authenticated against LDAP
2. User B has a normal ownCloud account
3. User A shares a directory D to user B
4. User B syncs using his or her ownCloud client , D is downloaded
5. The LDAP server is rebooted, hence the connection is lost and A is unable to authenticate
6. The ownCloud client of user B notifies the user that D has been unshared and deletes D from disk
7. LDAP server comes back online
8. Shares are restored
9. User B needs to redownload D

The problem is that D contains about 20 GB of files, and these 20GB are added to our allotted network bandwidth. Consider you need to reboot LDAP quite often, it always causes those 20GB to be deleted and redownloaded a couple of minutes later.

The issue names no files, tests, or entry points. Start by reproducing the described LDAP outage with an LDAP user sharing a directory to a local user, then trace what happens to the share while LDAP is unavailable. Done means the local user's share is not removed and does not trigger a delete and redownload when LDAP returns.