Your fireblend goes off 1% of the time, just that the description lied saying 10%. It's the script that's accurate and the description that is outdated. This is a wide spread svn update that all autocasting equipment and all item droping equipment is divided by 10 in most cases (some divided by even 500. I'm looking at you, electric eel).
There is no "duration" parameter for a skill (plus cast time is 1000 meaning 1 second anyway) in item if it's autocasting.