The more complex a map is, and the tighter the schedule, the easier it is to miss spots like those. Although it doesn't seem to be even noticeable until you brighten things up that is, so that one was particularly easy to miss.
When I do basics at some geometry from a random map, I always select some texture first for getting rid of that ugly jelly. When brush is being born I set textures before adding next brush. In this way you will never have empty borks. But default mapping style was different - let's rush this and release a crap which will stay rammed 30 years from now on and it will be an usual useless forum debate - no one from factory will fix this. And as you can see I'm not lying.