Is system() output guaranteed to appear in order?

[Ed Morton]

I thought I remembered running an awk command like (simplified example 
of course):

   seq 5 | awk '/3/{system("echo foo")} 1'

and seeing output like:

   $ seq 5 | awk '/3/{system("echo foo")} 1'
   1
   2
   3
   4
   5
   foo

instead of:

   $ seq 5 | awk '/3/{system("echo foo")} 1'
   1
   2
   foo
   3
   4
   5

but right now I can't reproduce that and I'm wondering if maybe I'm 
misremembering or just haven't hit on the right scenario. Is the output 
of a call to `system()` guaranteed to always appear inline among the awk 
output at the location where it was called or does it depend on the 
command you're calling or some environment settings or something? If the 
latter, what would be an example of that?

    Ed.