Photo Paint display 'colour depth' problem

I've started using Photo Paint X6 and I have a strange problem regarding the way images are displayed. I'm hoping someone can help otherwise I'm going to have to go back to a previous version. (I appreciate X7 is out but my PC isn't brand new, there's the cost and I don't even know if that would solve the problem).

The image displayed on my monitor, only in Photo Paint, is 'compressed'. It looks slightly posterised, perhaps as if the number of colours in the image were reduced.

 

I have a Viewsonic 24" running at 1920x1080, 32 bit colour. The number of colours in the image I'm looking at is about 125000. Skin tomes look ok, but for example, a black curtain behind looks very odd.

You can see the example here

http://postimg.org/image/ypogzc2d5/

The only thing I could think of was screen dithering, but thats greyed out. Any suggestions as to why this is happening would be appreciated.