Bug: The downward pointing error bar can be too short when the top error bar is clipped at the maximum axis range.

On XY graphs created by Prism 6 and 7, win and mac, the downward pointing error bars can be too short when:

• Error bars represent SD or SEM
• The Y axis is linear (not log)
• The top of the upper error bar is clipped at the upper range of the Y-axis. 
• More than half of the upper error bar extends beyond the graph limit. 
• This can happen even if you plot downward pointing error bars only and don't show upward pointing error bars. What matters is if the upper error bar would be off scale if it were plotted. 
• The shortening can be trivial or severe.  The shortening will be severe when the point is very close to the top of the graph, so most of the upper error bar is clipped. 

The length of the bottom error bar when the upper bar is clipped is equal to the shorter of: the proper error bar length, and the sum of the distance from the point to the upper edge of the plotting area plus 1/4 of Y-axis length.

To bypass the problem, go to the Y-axis tab of the Format Axes dialog and increase the upper limit of the Y axis so the top error bar is not clipped, or at least so less than half of it is clipped. This means set the maximum range for the Y-axis to a value greater than every Y value plus half the corresponding error value.