[Edi]

Yes, it skips them permanently. They are never targeted despite being eligible. For the purposes of the site search algorithm, these provinces do not seem to exist at all.

It may be a combination of factors and related to how Dominions perceives province borders. Red color in borderlines helps it determine provinces more accurately and Jason Lutes's maps all use the white dashed lines for borders, so that could be an issue. I mainly play on his maps. In Glory of the Gods MP version (the one with fewer provinces) there is an area just northeast of the convergence of the mountain ranges, around the gap that allows access southeast from the central plains, where some provinces sometimes exhibit similar behavior.

Though admittedly I have not seen this behavior as much after the search algorithm was changed. Most of my observations were from earlier, but it's happened to me even after that.