Full disclosure: I’m running a dev version right before .5 came out; it’s based on code circa 08th May. That said, I don’t think the “nothing” mapgen problem has been fixed yet, so hoping this helps.
Over in the screenshots thread I documented an extremely profitable Portal In.
Aside from the clear glitch (21 is a little too many Marloss Berries, and they ought to be on the Marloss Bushes), I noticed that it might be a clue to the blocks of “nothing” that show up on the map. On the approach to that Fungal Bloom, I encountered a few grackens, a Blob, and two of those “kretch” or whatever things stationed around a blank square of nothing.
I believe the square was the same size as that Portal In I encountered–didn’t think of it until afterward, though, so no screencap. The save I linked over in Shoes’ thread ought to be able to head over and check out the area, if anyone’s interested.