Why click to knob of NSSlider changes it's value?

FROM : Andrey Tverdokhleb
DATE : Sun Apr 29 06:37:16 2007

May be this is a stupid problem, but I just can't find a solution and 
hope somebody here knows what to do.
I have a simple NSSlider, min: -40, max: 60, 11 ticks, continuos, no 
sticking to ticks. Starting value is 0.
When I click knob of the slider for the first time it sends value 
-0.81081032752990723 through bindings. When I click it again it 
doesn't do this. If I change it's value to 0 programatically and 
click the knob again it sends -0.81081032752990723 again. What I 
don't understand why it's changing value on simple click considering 
that sticking to ticks is disabled. I tried to change amount of ticks 
- doesn't affect anything. Changing range changes that number, but 
the range has to be (-40; 60).

Thanks,
Andrey