Problem with a vertical UISlider with custom images

So i have a custom UISlider. It's vertical (i did it with the +270° technic). I have 3 images, respectively for the minimum value, maximum value and for the thumb. Everything seems good but i have problems with the extrema values, as you can observe on the screen capture (even though it's a little dark).

The slider on the left is perfect ! Both end of the sliders show the images perfectly and the cursor (thumb) is perfectly cutting the slider in 2.

The other two sliders on the right shows a similar issue. We can see that, when in extrema value, the cursor is not well located (there shouldn't be any part of the image below or above the middle of the cursor !) Oo More to that, let's look at the right slider (with minimum value). We can see that image has been cut on the bottom ! Indeed it should be close. It's the same thing for the maxi开发者_如何学JAVAmum value, the image looks like it's been cut.

I looked at the bounds of the slider view by touching it at both ends and looking at its coordinates. The slider was defined with a height of 300 but i can perform touches at coordinate 307, or -6 !!! I don't really understand why..

For more information, coordinates form 300 to 310 represents the maximum value i defined and negative coordinates (from 0 to -10) represents the minimum value. -> So We can notice there's a difference of 10 at both ends.

Please help ! :s