"Dead" below a certain point

[Mark179]

I've got this little test map set up; it's an atmospheric, foggy forest at night. However, whenever I walk to a part of the terrain that is lower than a certain point, I am unable to control my character, and must left click to reset back at the spawn point. Is there an automatic killbox below a certain point?

[taz1004]

View - World Properties - Zone Info - Kill Z

Set it to large negative number