When configuring the List Git Branches Parameter plugin, the value for the List Size field that's available when clicking the Advanced button cannot be changed. A value can be entered in the field and the job can be saved, but the value isn't applied to the field upon saving.
For example, if the List Size is set to 5 by default when creating a job, changing it to 0 should cause the field to become a dropdown, but that doesn't happen. If the value is changed to anything other than 5 and the job is saved, clicking Configure immediately after saving shows that the value has been reverted back to the default value of 5.
If the List Size is changed in the job's config.xml file and the Jenkins service is restarted, the field displays correctly, but it only displays correctly until the job is configured/saved again (it doesn't appear to matter what is changed in the job), at which point the List Size reverts back to the default value of 5 again.