As mentioned in #893, the comment highlighter has some pretty strange interactions with text posts, inconsistently highlighting terms.
If using the expando to view the contents of a text post, highlighted terms will be highlighted. However, if you click on a post, terms in the text post will not be highlighted... unless the post was removed, in which case highlighting in the text post will occur until/unless the post is approved. Non-actioned posts also do not receive highlighting when viewing a specific post (that is, clicking on the title to view the post with comments, not using the expando)