Slider getting smaller!?

Hello again :slight_smile:

First of all, I am working with this now in Real Studio 2012r2.1

I have problem with Slider. I have Canvas, Button and Slider. When I change position of Slider and click on Button, I need to move Canvas above the Slider position. I am calculating how much to change Canvas.left, but it seems that Slider is smaller than it should be. On this image you can see what is problem, I added two Rectangles and you can see that the slider is really smaller. Can anyone explain why is this happening?

Thank you