I've got this surface that is flagged correctly, as impassible, and no errors with the consistancy checker. In game I can walk through it and walk off the map. I don't know why it's doing this. I would just cleave the sector off a bit to make a new one, but it makes the new surface non-convex and I can't cleave it to be convex. Someone please help.

Thing just get stranger and stranger....

Try deleting the whole sector and rebuild it, if possible. Only shot I can think of.