Default VPN issue 4.4.2

I have a no brand galaxy s4 and lasy week I did OTA update to 4.4.2.
I noticed a vpn issue: when i try to connect to vpn pptp at work, the phone establish connection but no data is routed from /to the phone.
I tried to change username and password, even on the router at work, but it's always the same.
I read on the Google forum that it's a known bug from last November but I've never seen a solution. Some people tells that it's a bug in kitkat where mss/mtu are set too high to make vpn connection work.
Please can anyone help me?
Thank you

Alex

Inviato dal mio GT-I9505 utilizzando Tapatalk