The y-axis scales can now be fixed just like the x-axis scales.  Choose
YaxisLimits from the context menu when right-clicking on a histogram frame and a
small dialog box will open in which you can enter the min and max values.  If
the frame is part of a multipad canvas, all pads on that canvas will be redrawn
with the new scales.  Choose YaxisLimits again and click on the Unzoom button to
unzoom all pads on that canvas.