Peter.
Did you checked whether you can employ socat instead of PTY's? So, now you're running Debian-7.7?
Take a look at my site: http://sp2l.ampr.org to see what ham soft is running.
I have LinuxLite and Ubuntu-14.04 in VirtualBox Had not too much time to play with, yet...
Best regards. Tom - SP2L (ex sp2lob)