BlackBerry: Flickables and subclasses exhibit "laggy" scrolling behaviour

Using the blackberry platform plugin, behaviour of Flickables and related controls such as ListView and GridView have poor responsiveness during scrolling. I've taken to describing it as being like having a heavy weight that you're trying to drag around using a spring: it lags behind at first, then catches up, and if you change directions it carries on for far too long before reversing.

The QML code here can be used to demonstrate the problem: http://pastebin.com/qm7UZgDL

I've narrowed this down to commit da06e593d744c7edde3df934ecbc0875f98a156a where the screen event handling was redirected into the bps event loop, possibly with other changes though I haven't reviewed the diff in detail yet.

The previous commit a28f29270611247775a43e99525c18c7030e1488 does NOT exhibit the same laggy behaviour.

Several others have reported the lagginess independently, and one person had narrowed it down to code enabled using Q_OS_BLACKBERRY. He disabled that define on the latest code and the laggy behaviour went away.