Highlighting should work with the query, showing why the page matched not in addition to the query, showing, BTW also where the word is stemmed, even though the search query syntax explicitly requested non-stemmed.

When stemming is turned off by placing a word in double quotes, the pages are correctly listed, but on the search results page, sometimes stems in the snippet are still indicated in bold. This only happens when turning off stemming of the base word.

Matching works perfectly when turning off stemming for the word that is not a base word.

Searching for "clouds" (in quotation marks) gives

cloud clouded and clouds

as it should. But searching for "cloud" (in quotation marks) shows

cloud clouded and clouds

as seen at "cloud" prefix:user:cpiral.

Because match highlighting is used not only for location, but also for learning and teaching, documenting and bug-finding, this will eventually need fixing in order to teach what "exact phrase" means. Match highlighting in general is esp. important for trials in a sandbox.