Using Theme Studio 2.2, creating themes for Nokia 6280 (firmware 3.81)

I have created 2 x 24-bit PNG files as background images for form highlights, and added them to my theme in Apps > Forms. The images appear OK in the Studio, but when the theme is uploaded to my phone, they don't appear - the default Nokia background images appear.

It appears my images are ignored.

Has anyone been able to change these successfully, or can't it be done?