Moving selection range start markers in timeline is "jaggy"

1. Profile some QML application
2. Click on the "Select range" button
3. Create a range bzy clicking and dragging in the timeline
4. Move the start marker of the range

The start marker doesn't move smoothly with the mouse, but skips back and forth. This is because the marker's point of reference is the range itself which is being moved while the marker moves relative to it. The same behaviour can be seen in the overview panel at the bottom.