There is a bug in the current implementation of the tasklist macro that allows duplicate items to show up in the list if they have trailing spaces. So "apple" and "apple " would be erroneously considered different. When these similar items are marked as complete in Confluence, two entries are inserted into the OS_PROPERTYENTRY table. When these entries are exported to XML however, the trailing spaces are removed, so the second item is actually written to the XML file as a duplicate of the first. When this backup is restored, you will get a SQL duplicate key exception as Confluence tries to re-insert "apple" (without trailing space).