This is based on feedback from two developers in the Atlassian Community: https://community.atlassian.com/t5/Jira-questions/dialog2-aui-select-problem-with-aria-hidde/qaq-p/685426

Outside of Jira, an autocomplete control in an AUI dialog only fires its change event once.

In Jira, in any kind of dialog – either JIRA.FormDialog or AUI's dialog – it fires three times.