Highlight results not working well

Into the search results page the highlighter process is failing because it uses partial words. For example, I search “Paint the library” as a search phrase. Into the result page I can see words like “theme” and “there” or many others, being highlighted because they contains “the”. But I believe that the search should be using only the whole word “the”, so please, correct me if I’m wrong.

Another example. If I use the search phrase “This is a house” I could expect that “is” and “a” be removed from results because they are very common words, or at least that the word “a” doesn’t be used to highlight all “a” characters being present in results or all words that contains “is”. It doesn’t have sense for me. The word “a” should be highlighted only if it’s a isolated term and NOT a character inside any word.

I’ve tried in the past to remove common words from the results by using the banned words feature present in the plugin (I know that it’s not inteded to work that way, but to avoid non politically correct words), but without success. The plugin fails to exclude the words in that list and it’s even worse when there are accented chars. But also it’s highlighting partial words in a wrong way from my point of view.