You shouldn't need to do it, but it least it gets you past the problem. I've no idea what the browser does that causes this. It'll get fixed magically at some point in the webkit code, but until then it'll happen from time to time.
Usually the methods in this thread work. If it's a regular problem for anyone, consider using the @mjmooney tagging. Type @ and the beginning of a poster's name and click the poster when it pops up.