Possibly-simpler test case (open this; SaveAs .xlsx; File->Reload)
Test.ods (application/vnd.oasis.opendocument.spreadsheet), 8.53 KB, created by Jim Avera on 2012-10-02 20:50:23 UTC
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Creator: Jim Avera
Created: 2012-10-02 20:50:23 UTC
Size: 8.53 KB

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Attachments on bug 40070: 50191 | 61798 | 61799 | 68008 | 85062 | 85308