FileDialog qml component doesn't recognize updates to folder property

The folder property of FileDialog doesn't work correctly under OSX under several situations.

Steps to Reproduce:
1. Create a FileDialog component, for example:

FileDialog {
        id: importPlanDialog
        title: "Import Files"
        modality: Qt.WindowModal
        selectExisting: true
        selectFolder: false
        selectMultiple: false

        // this doesn't work on OSX.
        folder: "file:///Users/"

        onAccepted: console.log(folder)
}

elsewhere, call open() on the dialog. Choose any file and accept, then open the dialog again.

Expected Result:

• Platform native dialog should set the current directory to URL set in folder.

Actual Result:

• On the initial open() call the dialog will point and some unknown platform specific last opened location. It may be related to a setting in the app plist file, or it may be system wide. What ever it is, it will not be the URL set before the open() call, as stated in the documentation.
• On the second open() call the dialog will point to the users Document directory, again ignoring the value of the folder property.

It appears that on OSX the initial starting directory folder property is ignored on input, and is only updated on output.