Same as nubirthmedia and I am not using multisite
My site is here: https://scii.tv/
You can see that on the right hand side I have your widget and entitled it advanced search.
I put two test posts at the top that are only uncategorized and should never show up in a search (except a blank search).
If I choose any of the categories, the URL will change showing that it is only searching for the category IDs, but the results will always return every single post.
