What is the bug about:
Keyword gets duplicated even when the query is not modified.
As far as i can tell - cosmetic.
How to replicate:
Go to: https://careers.stackoverflow.com/jobs/tag/python and keep pressing
Search button. With each search there will be a duplicate python keyword appended to search box.
Best guess for what is causing it:
I think you have somewhere a piece of code that appends tag as a keyword without checking if it is already present. My reasoning comes from this url: https://careers.stackoverflow.com/jobs/?searchTerm=python not having the same issue - the tag is not present in it.