I've noticed that too. I was just looking up the level 10 mez to see if it was going to be more useful, and i was surprised to see 28 secs listed. I looked under this spell description and here we have 21 secs. From my (limited, lvl 6) experience its lasted closer to 3-5 secs somewhere. (feels like 3 but we all know that time is always shorter than you think in these cases) The level 5 mez is so short its essentially worthless.
I also noticed the level 1 mez that nobody will ever get ;)