Found it today from TN 1596479
If the Synchronize Contacts feature is in use in IBM Lotus Notes 8.x, then a user who uses a Location document to switch to another mail file can unintentionally replicate deletions to that other mail file if they have Editor with delete documents access. Conversely, any delete operations in that other mail file will also propagate when switching locations back to their own mail file.
To be impacted by this issue, the following must be true:
1) You must have this option enabled: FilePreferencesContacts->’Enable “Synchronize Contacts” on the replication and Sync Tab’.
2) You must be editor (or above) with delete documents access to another mail file/mail-in database.
3) You must have a Location document that specifically points to the other mail file.
4) You must switch to that location.
5) You must have deleted a mail message that went to your mail file AND the other mail file, thereby sharing the same document UNID.
6) The message must not have been deleted in the other mail file
