Game server Firewall issue

[ArtashesM]

Hi All,
I am trying to run a minecraft game server on a virtual server that is managed by Plesk 11.09.
So far I have configured the Firewall to accept the input (and just in case output ) from

tcp dpts:25560:25575
udp dpts:25560:25575

The game server currently runs on by default on port 25565. The issue I am encountering is in the following, when I connect to the server first time through a particular port the game runs fine, however in a few minutes it disconnects and I can not connect to it through the same port again. If I change the port and restart the server I can connect to it, but the same issue occurs again. So I keep wondering is there any other security mechanism running on a server by default that I am not aware of ?

Thanks in advance for your time and replies

 

[ArtashesM]

Help ?

Any help or a pointing into a direction where to look at would be greatly appreciated