My hunch is you're lucky to be getting that.
You probably shouldn't have removed the auto-flush line.
Of course we don't know if you're trying to bicirectional
line-by-line (a la expr or cat, autoflush is a must for this
kind of talking). If not and you're only doing something
like HTTP/1.1 you still really ought to have autoflush
but it's not the same. As you would get a multi-line output
from child per single input from you (as opposed to one-to-one
which is what you don't specify).