[Protect GUI , port 8888 from outside]

I like to protect my gui on my raspberry pi

i did the following for my firewall:

sudo ufw enable
sudo ufw default deny
//(sudo ufw deny 8888) <--- should be also included in default deny

The problem is that I can still with my firewall running access the GUI from another computer over the internet? That should not be? What is wrong in my settings.

I know that I can start btsync with a config file which does not allow gui access but this is good but I would rather like to block the 8888 port in the firewall as block the 8888 port on my router too to be 100% safe.

Why is the firewall approach not working? Is btsync messing with the iptable?

Thanks alot!