QML Canvas rendering bug with Threaded renderStrategy

I'm getting strange bugs when rendering to Canvas in Qt 5.0.1. Given this QML file:

import QtQuick 2.0

Rectangle {
width: 500
height: 500

Flow {
id: flow
Component.onCompleted: {
// Create a bunch of canvases dynamically and put them in the Flow

"1/2/3/4".split("/").forEach(function() {
function finishCreation()

{ canvas.width = 100; canvas.height = 100; var ctx = canvas.getContext("2d"); ctx.fillStyle = Qt.rgba(255, 0,0); ctx.fillRect(0,0,100,100); }

console.log("creating canvas");
var canvas = Qt.createQmlObject("import QtQuick 2.0; Canvas

{renderStrategy: Canvas.Threaded; visible: true}

", flow, "canvas"+Math.random());
canvas.onAvailableChanged.connect(function()

{ if (canvas.available) finishCreation(); }

);
});
}
}
}

(obviously this is a simplified example of what I'm actually trying to do; the above example doesn't need to dynamically create the canvases, but the actual thing I'm doing does, and it needs Threaded rendering to be able to use Canvas.toDataURL)

I should get 4 red squares. Instead, I get one red square, and which of the four squares renders changes from run to run. (See attached screenshot.) Feedback on Google+ suggests that some other people are getting four red squares as expected, so I think that this is a bug rather than pilot error.