As described in defect 62717 content type aren't always saved, it leads to unloadable document using org.apache.poi.openxml4j.opc.OPCPackage.openOrCreate(File) api.
@pouponbe you marked this as a regression but didn't indicate what version this worked in
It works with version 3.10.1.
Seems to report the same as bug 62717 anyway so not much use in keeping two bugs open for the same thing. *** This bug has been marked as a duplicate of bug 62717 ***