Schema processor does not reject xs:group/xs:sequence/@maxOccurs
The schema for schema documents states that a top-level xs:sequence, xs:choice, or xs:all compositor within a named model group must not have a minOccurs or maxOccurs attribute.
Saxon performs this check in the case of xs:choice and xs:all, but does not perform it in the case of xs:sequence.
A patch is being applied in the 9.5 and 9.6 branches. The error has probably been in the code for ever.
Test cases Saxonica/Complex/complex019 and /complex020 have been added to the W3C test suite.