Right, I tried this, and although obviously necessary, (I am after all swapping from write to read on an object that is something like a file handle.) sending an EOF after finishing the data write did not solve all the problems. At first it worked exactly as expected, then I increased the size of the data sent to 100k and this is what I got:

ssh created
ssh connected 
ssh authenticated
cmd is wc
intext length is 100000
      0       1   32768
remote exit status is 0 bytes returned is 24 bytes
[download]

Note that intext length is measured at the local machine, and the numbers come from wc at the remote end - it only got 32k. 24 bytes returned looks correct.

It WAS necessary to set blocking(1) (presumably the default would have been ok) , without this NO input at all was received by wc, but the process still ran and returned output , 0 0 0 in that case.

I tried this to another Ubuntu box with exactly the same results.

So Net::SSH2 still seems broken, but now in a way that is very similar to the way Net::SSH::Perl is broken.

Hmmm.