|I had responded. I'm not sure where it went, so here it is again:|
That's interesting. I'd assume it's caused by an over aggressive write cache scheme.
You could try a third party program like Sync.
Alternatively, you could try working around it by spawning a copy of CMD per line of output, like so:
cmd /c echo Hello World >> out.txt
cmd /c echo Flush me to disk >> out.txt