Changing Brightness causes Image Shift

Using Captivate cc, I brought in a .png image to a page on a project that is not "Responsive"; the courwse is meant for desktop use only.  The png image was a bit too light so I used the "EDIT IMAGE" feature and changed the brightness rating from 0 to a negative 10.  Making the change, the non-transparent portion of my image shifted from being displayed in the middle of the page to the top of the page.  The png. image is the full size of the screen (1024x627) positioned at X: 0 and Y: 0.  The X and Y stay the same before and after the change of brightness.  But the non-transparent portion of the image within the png suddently becomes displayed at the top of the page whenever I change any settign within EDIT IMAGE except ALPHA.  It is like Captivate diregards the blank portion of the image and shifts the rest up.  (FYI: changing the Alpha setting works fine.)  Changing the Brightness setting back to 0, bring the image back to it's proper position.

As a test, I created a smaller version of the same .png and Captivate does the same behavior but not as severe.  It moves the image about 3 pixels up and 3 pixels left. 

Does anyone know what is causing this strange behavior to PNG files and how I can make it stop?

Thanks