The problem of an extra border around exported DRGs that have had the collar removed is caused by the fact that DRG Quads are NOT rectangular in the UTM projection after their collar has been removed. Rather, they are aligned on lat/lon grid boundaries, which makes them a little bit skewed when viewed in a UTM projection. Because the base TIFF and JPG formats only support rectangular images, something must be used to fill in the areas around the quad such that the data fills a rectangle. This extra fill causes the border to appear.

The best workaround for this problem is to reproject the images to Geographic before exporting them to a new file. This way the quads will be rectangular and you won't have the extra border around the data. You can change the projection for viewing and exporting the data by using the Projection tab on the Tools->Configuration dialog. See the earlier FAQ question for more details.