large open square from surface to level 0

a large square hole from surface to level 0 opened up in an area i was minining, hadn't been there the last time i logged in, has lava, water, minerals, showing in sides of hole. when i mine a mineral or stone, the empty spot is black; if i put down a torch it only lights one square. But, if i disconnect and then reconnect, light shadings are correct but hole is still there. If i move out of that particular area, everything is fine. See also my other issue i created, which may or may not be related about not saving char work that has been done between disconnects.