Using the mouse wheel on the plot the whole plot (all axes) is zoomed.
The patch allows to use the mouse wheel on a single axis so that this axis is zoomed only.
Note: On CombinedXXPlots it seems that the anchor point is miscalculated. The anchor where the mouse wheel is rotated is not stable. But this happens also when zooming within the plot are (zoom on all axes). So this seems not to be a bug of this patch.