So, it appears that the default functionality for options/selections displayed in the Sprint field are recommended sprints (ones which you have recently viewed) followed by all other sprints in the instance (unless user begins typing the name of a sprint they want, at which point autofill will suggest sprints accordingly).
Is there a way to apply context to the Sprint field so that only sprints associated with a board in which the issue would be viewed are selectable? I have a user who says people are adding sprints to an issue that don't apply (as they belong to a board that the issue would not be displayed on), and this is messing things up.