This is the one problem I have with it, the onClick part. Sometimes I highlight text too (I have no idea why), and it is kind of annoying when it goes to a forum, that I didn't want. Otherwise the highlighting is great.
To fix those issue's just remove the onClick part, then they can still highlight the text, without clicking anything, and they can still click anywhere, it will only just still highlight. I'd say, re-apply and see how they re-act when it doesn't click-thru.