This has been a problem for a while, but I've just been too lazy to report it. Sometimes, if I highlight 2 or more words while reading an article, the mouse-over and link creation gets disabled. I think this only happens when one of the words is blue, and it doesn't always happen. Just sometimes. The work around I do is to close the page and re-load it. I don't know if it makes a difference, but I'm using Mac OS X, and safari.