REG: Jumps in Qt Quick animations when running at < 60 fps

When an animation in Qt Quick is running at less than 60 fps, it will run in slow motion and at certain points jump ahead in time, like it's trying to catch up with itself.

This did not happen in Qt 5.3.

See the attached example. The rendering in the background is arbitrary, this can happen with any Qt Quick app and without any FBO present. But in the example, the renderer in the FBO will delay for 64 ms each frame.

Run the application and click on the "Show Sidebar" button. This will animate the width of the sidebar from 0 to parent.width. In the beginning it will be really slow, and then suddenly jump ahead. At this point it will run at the correct speed but at the artificially reduced framerate.

If you run the same example with Qt 5.3 it will run at the correct speed for the full animation.