Diging yourself a crash- how was this not noticed?

I once wondered whether dig could be used to destroy actual walls.

So, I dug an edge-of-the-dungeon wall. Cool.

Then I tried to dig more, finding out that if you try to dig what's AFTER a edge-of-the-dungeon wall, the game will crash. I've done this numerous times, on different machines.

How was this not noticed?

Heh...I'm guessing for the same reason I never tried it...it just didn't occur to me to do it. Will fix.