If you have a maintainable collection like vendorHeader.vendorSupplierDiversities, where vendorHeader is a reference and vendorSupplierDiversities is a collection of vendorHeader there are a couple of
problems in the maintenance framework:
1) When canceling a document and confirming, class cast exception is coming from BusinessObjectServiceImpl#addMaintainableItemRestrictions. This is because vendorHeader is null and PropertyUtils does not handle that correctly
2) Required fields on collection not getting validated. This is due to the logic of MaintainableDocumentDictionaryServiceImpl:getCollectionDefinition. This method assumes that if the collection name contains a '.', then it is a collection of a collection. But that is not the case here.