Variable binding of a property of Map element causes unexpected result in executable model.

Issue

Building and executing a rule written in MVEL dialect that accesses a Map element and binds a property of the element to a variable in executable rule model, the bound variable is an unexpected value.

For example, when I build and execute a rule (*1) which uses a statement like (*1-1) with java code (*2) with executable rule models enabled,

(*1) rule

package com.example.reproducer

import com.example.reproducer.Car

dialect "mvel"

rule "rule1a3"
    when
        $car : Car( $supplierName : suppliers["transmission"].name )    // ..... (*1-1)
    then
        System.out.println("***** Action of rule1a3");
        System.out.println("***** $car: " + $car + ", transmission supplier name = " + $supplierName);
end
// suppliers is a {{Map<String, Supplier>}} type property of Car class

(*2) java code

Car a = new Car("A180");
Map<String, Object> specs = new HashMap<>();
specs.put("transmission", "8-speed automatic");
a.setSpecifications(specs);
Map<String, String> parts = new HashMap<>();
parts.put("transmission", "T8SAT");
a.setPartNumbers(parts);
Map<String, Supplier> supls = new HashMap<>();
supls.put("transmission", new Supplier("ABC Precision Instruments"));
a.setSuppliers(supls);
kSession.insert(a);

System.out.println("***** start");
kSession.fireAllRules(10);
System.out.println("***** end");

$supplierName value will not be "ABC Precision Instruments" (the name property of Supplier object) but "A180" (the name property of Car object) unexpectedly.

$ mvn clean compile exec:exec -DgenerateModel=YES
...
***** Action of rule1a3
***** $car: com.example.reproducer.Car@4b6690c0, transmission supplier name = A180
...