I need to create an image which is exactly 1024 x 1280 pixels.

I've set this as my page size however when I export it, the export dialogue box automatically resizes the image to 1024 x 1296. I have tried altering the 'Scale' when exporting as a bitmap, and the 'DPI' when exporting as a PNG but Xara insists upon constraining the proportions. How do I get around this problem?