Highlights query - returns too long a snippet

if i opt to search multiple words especially if enclosed in quotes as a phrase, i get random hightlights returned with huge blocks of text that far exceed the set fragmentsize...

its erratic in that it doesnt happen in all results but often enough to make the search results page look untidy and unreliable...

can anyone explain why this happens...

ive tried all 3 types of highlighting and it happens whichever i use....