When using clone stamp, after defining source, applying it turns image white

Hi, 

I've seemed to encounter a strange issue. When I use the clone stamp, and define a source within the image, then proceed to apply this source definition to the needed area, the ENTIRE image goes white. I cannot see the application of the clone stamp live, as the i,age is going white. 

After releasing the clone stamp, the image returns to view ( I can now see it ie: it's not white anymore), and the clone stamp application has been applied. 

What is causing this white out? I need to see the clone stamp being applied as I work.

I'm a novice, so I may not be understanding something very simple. 

Please help.

- J