Photoscenery: Cause of Line Artifacts?

I'm getting artifacts in the form of lines running through several areas of photoscenery I've created using maps2bgl. As an example, here's an area I'm working on. I've drawn a red line on the screenshot that parallels the 'seam' I'm talking about. At first I thought maybe this had to do with my water masking (I've had some issues with this which have been resolved by scrutinizing the perimeter edges at high magnification for any artifacts that might screw up the complete selection of an area to be masked), but it appears the gap runs through the land portion as well. I've noticed these annoying gaps in several areas I've created along the east coast of the Big Island of Hawaii. I've yet to establish any pattern regarding the whys and wheres. Seems kind of random. Any ideas as to what might be causing this anomaly?