I can see the same behaviour here. I only get a few of my PROJECT headlines
if org-enforce-todo-dependencies is t; I get all of them if it is nil.

My value for org-todo-keywords is:

((type "TODO" "NEXTACTION" "INPROCESS" "WAITING" "NEEDSPREREQ" "|" "DONE"
"DELEGATED" "CANCELLED")
 (type "PROJECT" "|" "COMPLETED")
 (type "SOMEDAY" "MAYBE" "|" "CANCELLED"))

The odd thing, to me, is that this doesn't seem to affect e.g. WAITING or
SOMEDAY tasks, though those are not likely to have children, which PROJECT
headlines certainly will.

-- 
Jason F. McBrayer
http://jfm.carcosa.net/