I think this is pretty normal. I've seen basal keiki on many non-Dtps
plants, and I currently have a Phal that's doing the exact same thing as
yours. Plants that are croaking do make keiki as a lost shot, but it
also makes sense that if a plant was doing well and had lots of "extra"
energy, it would invest it in some progeny. It was extremely lucky for
me because soon after, the primary crown got rot had had to be cut back!
The location isn't odd, as I've seen that too.

Cheers,
Xi

Up until today I had assumed that Phal's basal keikis always start at the
base, at the bottom of the plant. I had assumed that non-basal keikis always
grow from a flower spike and not from the main stem where the leaves come
from. Also I had not expected any of my non-Doritaenopsis to have a basal
keiki, unless the plant itself was in danger of croaking, whereas this is a
very vigorous plant. Were my assumptions just wrong? Or is what is happening
here unusual?

Joanna