Prior to an edit, this question was posted with no content in it, both in the title and the question body.
The explanation to reproduce is provided in Temani Afif's answer.
Since this was discovered, similar text fields around the site have been found to have similar issues and they are outlined in the answers below.
Note from Catija:
While we appreciate all the effort y'all have gone to to test and find places this is possible, we'd like this question to be understandable so that seeing it doesn't cause confusion. Feel free to add additional information to this answer but please leave the question itself as-is. Also, while y'all are free to continue to seek out these issues, we hope that you would all refrain from actually abusing this feature.