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In the Microsoft ModelGroups test set, test <test group="mgO013" name="mgO013"/> The expected result is that the schema is valid. However, the redefining group is not a valid restriction of the group that it redefines. The redefining group has a content model that requires a single e1 element, whereas the redefined group is effectively empty.
This test should indeed be invalid. This is due a bug in the packaging process of Microsoft schema tests.