Unable to forward ports to VM

[buiz_]

I'm running the latest firmware (4.3.3) and VS 3.0. I have an Ubuntu 14.04 VM running in VS that runs Quasselcore that listens for connections on port 4242. I am able to connect to the service when I'm on my internal network, ie the port is open and the service is working fine. I have set my router to forward port 4242 to the VM, but I am unable to access the service from outside my network. For some reason my router is unable to handle port forwarding to my VM. This was not a problem before I upgraded firmware from 4.2.x and with it VS. UFW (firewall) is not running on my Ubuntu VM but even if it was it wouldn't matter because I can access the port just fine when I'm on my internal network. I tried messing with virtual switches and its setting but all that got me was a couple of hours work restoring my NAS's network settings. Is this a bug?