Matt beat me to it. perhaps these will help you understand a bit better, also, this is how v11.1 worked too, so I don't fully understand the extent of aggravation conveyed in your post.
katie melua contains an 'i', her album contains 'search', so why is it wrong that it should be listed by your search?
perhaps if you had wrapped the strings in quotes your results would improve?
i would expect bad to the bon to return all bon jovi tracks, as well as any album that contained the word 'bonus'
again, wrap in quotes.
as for the hello search, I'd say you are getting positives from fields that are not visible in your scheme. I'm not able to rattle off a comprehensive list at this time, but, certain library fields are flagged as "default search" items. This means that all of those flagged fields are searched when you don't specify a field in the search box.
ie: ar=bon would search for artists that contained bon, but if you just type bon, all the 'default search' fields are parsed for bon
better now?