its not a fork of ksh, its a fork of an open source ksh clone called pdksh that predates AT&T ksh open sourcing, and is frankly kinda crap. OpenBSD has improved it, but compared to real ksh its lacking quite a lot, most painfully sane substrings.
Right. In the spur of the moment I wrote "a fork of ksh" as in "a shell (mostly) conforming to ksh' specs", which is technically incorrect -- the worst kind of incorrect.