Image swap based on attribute selection?

In our install of 1.3.9h we have an effect that swaps the main product image with that of an attribute when the attribute thumbnail is clicked.

At the same time, the attribute selection box is altered to reflect that attribute

(So clicking on the red swatch/thumbnail swaps in the red version of the product images and also changes the attribute selection to red.

Works great. I'm assuming it's a regular ZC plugin, but I'm not positive because I'm not the original developer.

Here's my problem -- if the customer selects the attribute using the drop-down menu (and not the swatch), the main image is not changed.

Is anyone familiar with this effect and if so, is there a way to have the attribute pull down trigger the swap as well as clicking on the swatch?

Thanks,

John