Mark the word - some marked words aren't marked

I found out, that in a "Mark the words" exercise some of the marked words were displayed together with the * that should have been invisible. As the marked words all came in pairs, like in *have seen* I eventually found out, that it's simply necessary to have another word or letter which follows the second * and everything works fine.

Here's an example in case you have trouble understanding:

This doesn't work:     I still *haven't found*

                                  what I'm looking for

This works                :I still *haven't found* what I'm looking for

I just wanted you to know about this. Thank you.