Function redefinition in vm.runInContext

Possible bug of iojs or perhaps v8?

    var vm = require('vm'), ctx = vm.createContext({});

    vm.runInContext('function test(){return 0}', ctx);
    vm.runInContext('function test(){return 1}', ctx);

    var result = vm.runInContext('test()', ctx);
    // returns 0 in io.js, but 1 in node.js

Tested under win7 x64 and linux.