Multi Instance support can be easily broken by different dataInputAssociation order, since collection expression is taken from dataInputAssociations without verifying the values given in loopDataInputRef, github reference: https://github.com/droolsjbpm/jbpm/blob/master/jbpm-bpmn2/src/main/java/org/jbpm/bpmn2/xml/TaskHandler.java#L195

Moreover since jBPM is now more strict about variable types multi instance needs to deal with data types as well to avoid problems with recognizing right data type.