add the lengend icon to the click event not just the label
I had the same problem. Luckily this can be fixed relatively easily.
(Hmmm, I tried to post the patch but the comment system won't let me.)
A patched version of highcharts.src.js can be found at http://nerzhul.miuku.net/js/highcharts_clickablelegend.src.js
Just compress it with your favorite JS compressor tool.
everyone i show my app to uses tries to click the icon (the colored block) instead of the series label inside the legend