Strange background behaviour

I'm adding the option of choosing the background on one of my gadgets, with 3 backgrounds to choose from. On my gadget I have areas that change the cursor to the hand with css and have onclick listeners to perform an action when the area is clicked.

The strangest thing is happening, though. On 2 out of 3 of the background images, these areas function correctly (100% perfectly). On the 3rd background image, they don't. The hand cursor only appears on certain parts of the area and the onclick handler only functions when the hand cursor is visible.

I really don't understand this at all, they're just images, right How can the background image have an effect on the elements of the page To start with, the background was set using System.Gadget.background, but I've changed it to use g:background in a bid to get it working (no improvement).

Anyone else know what the problem might be

Andy