Issue Statistics Gadget has inconsistent behavior

Issue Statistics gadget does not handle a select list as the statistic type with natural order sorting. Result is some of the options are missing.

Steps to reproduce:

Create Project1.
Create Project2.
Create Field1 of type Select List, in my testing the search template did not matter.
Create a separate context for Project1 and for Project2. Include all issue types for both.
Add a set of options to each project. They should not overlap in name. When I did this, I had 5 options in Project1 and 6 in Project2.
Create multiple issues, until most of the options have been used 2+ times. Leave some options completely unused in each project. Project1 had 2 unused, and Project2 had 1 unused in my test.
Create a filter such as "project in (Project1,Project2)" and save it.
Create an Issue Statistics gadget. Select the appropriate filter, set the statistics type to Field1. Sort by Natural. Sort direction descending. Show resolved issue statistics Yes. Refresh Interval never.
Notice that only some of the values from Field1 show up.
Change the Sort by to Total and all of the values show up.

QED ∎