When a chart have long labels on the X axis (like date and time) the zoom is not accurate on the horizontal extents with both mouse wheel and drag area.
The reason is probably that the screen coordinates of the selected area are not mapped correctly on the X axis. The mapping works fine for tooltip.
You can verify this behavior in the attached Solution. In the images you can see the selected area (01), that the zoomed area is a region with no points (02) and the actual position of the points.