Disable swatch on product list changing main product image.

Hi There,
My theme has a function where it shows the first woo commerce gallery image on roll over.
I’m also using the show swatches in product list function from your plug in.
What I’d like to try and do is stop the main product image changing when the swatch is selected.
I have ‘change product image’ set to ‘not change’ in the custom attributes settings, but this doesn’t make any difference.
Anything I can try?
Thanks
Dan