We are populating our user profiles with data from AD and a BCS connection to a LOB DB.
We perform an overnight incremental UPS synchronisation of data from AD and the LOB DB system.
This works fine in normal operating conditions, however we have noticed that when the LOB DB is not available then when the incremental synchronisation runs the fields in the User Profile that are mapped to the BCS LOB DB have all their data removed.  There does not seem to be any error handling in the UPS connection for BCS.
Is there a configuration change or something we can do to prevent the synchronisation deleting data when the BCS LOB system is not available? We want the situation if connection the database fails then the data in the profiles remains until the connection to the LOB DB system is restored.
  

Hi! I know this is an old post, but I'm having the same issue. Have you found a solution yet?