If you have any Issue Picker scripted fields that are set to allow multiple issue selection you will see an entry in the issues change history for any change made to the issue and even if the user just opens an issue for edit, changes nothing and clicks update.
Steps to reproduce:
- Create a Scripted Issue Picker with the "Multiple" checkbox ticked
- Assign it to a valid screen for your project
- Go to an issue and click edit
- Change nothing and click update
- Go to the bottom of the page and select "All" under "Activity" and you will see an entry for the Multiple Issue Picker field
Note: this is possibly related to this other issue here