Slideshow display problem

I'm not sure whether this is a javascript or CSS related problem so sorry if I've posted this in the wrong place.
I'm modifying a slideshow plugin to fit my website and have changed some of the dimensions of the slides. Now the next slide is coming in from the wrong position on the right hand side.
I'm not sure how to fix this, can someone please help?

http://ah.mjtippet.com/

That is a CSS issue and is because the button has a higher "z-index" value than the slide image.

The button is not the problem. It's the fact that the next loading slide is arriving at the wrong position but I don't know where to find this.