I don't know if this is a bug, but I did an Advanced Search looking for a family wrestling story per a request on the Forum. In the "Story Text Search" I entered "wrestling mom" (once with the quotes and once without them — I got the same two results both times) and changed "all words" to "exact match." I got two matches, but neither was an exact match of what I put in the text field.
One had "wrestling, mom" highlighted. The comma should not have made it an exact match. "wrestling, mom" and "wrestling mom" are quite different (like "Let's eat, Grandma" vs "Let's eat Grandma").
The second one highlighted: wrestling," Mom — which was followed by an unhilighted "said." the ending quote wasn't highlighted, but the comma was. It also had the word "wrestling" without the "mom" highlighted twice in the paragraph.