I tried something. I added a tee to the remote command to log its output in a file (on the host, a different file for each call).
It appears that it is traceroute that is mixing up its outputs on the host; Net::OpenSSH is working fine.

For info, what the recorded file through tee is returning (second line is wrong and belongs to another traceroute call, but the hop number is wrong as well as in the other call, it is hop #1, this ip is never hop #5). 
root@HERMES:/tmp/mnt/sda1$ cat test_77.95.71.196.tee 
traceroute to 77.95.64.123 (77.95.64.123), 6 hops max, 38 byte packets
 5  10.2.0.211  8.592 ms  2.467 ms  2.718 ms  2.530 ms  2.561 ms  2.56
+1 ms  2.687 ms  2.749 ms  2.405 ms  2.561 ms  2.562 ms  2.562 ms
 6  77.95.70.196  18.432 ms  18.244 ms  18.431 ms  18.119 ms  18.463 m
+s  18.213 ms  18.619 ms  18.151 ms  18.369 ms  18.119 ms  18.556 ms  
+18.682 ms

[download]
What the traceroute should return:
root@HERMES:/tmp/mnt/sda1$ traceroute -w 1 -f 5 -m 6 -q 12 -n 77.95.64
+.123
traceroute to 77.95.64.123 (77.95.64.123), 6 hops max, 38 byte packets
 5  77.95.71.196  18.806 ms  18.244 ms  18.619 ms  17.995 ms  18.807 m
+s  18.463 ms  18.495 ms  18.307 ms  18.744 ms  18.276 ms  18.588 ms  
+18.307 ms
 6  77.95.70.196  18.588 ms  18.276 ms  18.432 ms  18.089 ms  18.588 m
+s  18.088 ms  18.463 ms  18.119 ms  18.432 ms  18.151 ms  18.588 ms  
+18.181 ms

[download]

So this traceroute does not work properly when called multiple times at the same time.
Net::OpenSSH output is similar to the one on the tee file, so behaves as expected.

In reply to Re^2: net::OpenSSH several commands, stdout are mixed up by Bolemo
in thread net::OpenSSH several commands, stdout are mixed up by Bolemo

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