Drag/Select with multi-touch trackpad troubles

I'm loading the following d3.js example in a QGraphicsWebView
http://bl.ocks.org/mbostock/1667367
and have troubles using the MacBook multi-touch trackpad on the bottom panel of the graphic (the one use to make a zoom/slide on a subset of the data) by tapping/dragging the trackpad with 2 or 3 fingers.

It works well with a regular mouse or actually clicking the pad (not tapping it).

Why would it be a bug of QWebkit and not of d3.js? Because the same example works well with multitouch track by using Webkit with Google Chrome 25.0.1364.172 and Safari 6.0.3 (7536.28.10).

Defining the macro TOUCH_OPTIMIZED_NAVIGATION doesn't solve the problem.

Strangely, loading Google Maps works well (better than in Google Chrome where zooming gesture results in increasing text size.

Attachments:

• an example created with Qt Creator HTML application wizard,
• trackpad Settings screen shots.

Thanks,

Vincent