A lot of items say something like "-30% flee" when they mean "-30 flee"; this stems from the fact that if, say, you had 50% flee against some monster, and put that on, you'd have 20% flee. So you've lost 30 percentage points from your chance to flee that monster. I think the problem is that "flee" is used to mean two different things - the number in your stat window, and the calculated number for your rate to dodge a specific monster that's attacking you.
That's why there's confusion about this. "-30% flee" for something that means "-30 flee" is absolutely not correct, though.