Paint Shop Pro :: Getting Color Bars Across Photos

I am having a rather strange problem with PSP X14. I will describe my general workflow and where the problem occurs.

I do some editing to my photo and save it as a full size image. Next I resize it to a much smaller version for use online. I have no problems at all with these two steps. Next, I cancel the resized dimensions and resize it again to a file closer to the original size, after I sometimes sharpen it and add a canvas. Many of the thumbnails for this last step have horizontal color bars across the bottom of the thumbnail, ranging roughly from 1/16 to 1/3 of the image size. When I hit on it and open the file, the bar is not there. I tried opening this thumbnail in another photo editing program and when I have access to the thumbnails for opening, that bar is there on select images, and when I open the file, it's gone. Unfortunately I haven't had the opportunity to try printing it yet.

I've been following this basic formula for preparing and editing photos for a very long time and haven't had this problem until recently. And it's random, as not all images have this problem. I tried changing this process and reopening the full size file that has been edited and resize that one, but am getting the same random results. I have no problems with the thumbnails for the full size and the first reduced size images.

I have been a long time user of PSP...since v.7 and upgrade versions regularly. I'm running Windows 7 premium, 64-bit on a laptop with an Intel i-7 processor.