I have found an issue with Windows 8 and Soldier Front disconnecting if you are using mumble while playing. When you connect to mumble and then log on to SF, you will be disconnected.
How to avoid disconnection:
1) Launch Soldier Front
2) After Soldier Front is loaded, Right Click Mumble.
3) Click "Run as Administrator"
4) Click "Yes"
5) Connect to Mumble
6) Play SF Free from Disconnection!
In other words, you need to start Soldier Front before you launch mumble. Hope it helps!