Glo Highlighting text only works for a while

Anybody else seen this problem? Highlighting text works for a while in a book (you mark the text, and hit the highlighter icon) -- but after a while, it stops working (hitting the highlighter icon does nothing; the text doesn't highlight and no entry appears in the list of annotations). I've seen it in a couple of books now, most recently the Canadian edition of THE WISDOM OF PSYCHOPATHS by Kenneth Dutton. It's very frustrating. Sometimes, the capability returns, and sometimes it's gone for good for that book.