Unlike Edit Message, the Edit Poll screen allows you to change the subject line.
If you do change it and click Update Poll, the subject line of the topic is unaffected. But the change is stored somewhere, because if you click Edit Poll again, the change you made shows up, and these changes do appear in the activity log.
It would be more straightforward (and consistent with Edit Message) if this entry field was simply disabled and you had to click on the "Topic Properties" button to update it.
Thanks for your consideration,