--Edited--

It appears that you are right, I was able to replicate the issue by running the commands from the command-line. It also pointed out that the full output isn't there as previously thought.

I tested this on a friends router with a different version of the OS, same problem. I then changed the command to another one that has long output and I got the same results.

I then copied that output to a file on my system, and got the script to issue a cat on that file after logging in. This worked as expected.

To me, this definitely rules out the openssh libraries, the Net::OpenSSH module and perl it's self. It appears that the problem is with the amount of lines or data the router needs to output back to the script.

So I guess, to some degree, I am back to square 1. I will need to figure out how to interact with the router using expect (since Net::SSH::Expect worked for this task..)... oh boy...