eugenmihailescu on "[Plugin: Relevanssi - A Better Search] Highlight+WP Super Cache=>persistent highlighting"

If WP Super Cache is enabled and if Relevanssi is set to highlight the result, the search for a keyword will display the result hightlighted. Good!
What if you visit the same page 1" later via direct link (not by searching). We will se that word hightlighted and it will persists until the cache is rebuild/cleared.

http://wordpress.org/plugins/relevanssi/