The original setup claims it supports multiple machines accessing the same server, using the same port but different users. See the first link above.
For some reason when we ssh to two different users but on the same port from the same network, we're crossing paths. That means:
If two users exit -
a ssh-es via port 999 to server.com and
b ssh-es via port 999 to server.com from the same network, if
rmate file on his terminal,
b gets the file in his text editor in addition to
Hope this make sense - my networking game is not on point.