Please note that internally WinpkFilter driver uses a limited buffer pool used for all packet related operations. So, an example, if you set a network interface into the tunnel mode and won’t read filtered packets from the driver then the number of queued packets grows up to the buffer limit and as soon as the limit is reached the network operations are blocked for all network interfaces (network freeze). So if you expirience the network freeze it is more likely to be a bug in your application. There are many WinpkFilter based applications on the market, and if it would be a kind of hidden bug then you won’t be the only one who expirience this.
By the way, what kind of driver you have installed on your server? NDIS IM or NDIS LWF? Both drivers can be used on WIndows 7, but they are different by architecture. So if you try another one there could be a difference in behaviour. However, if this is application bug then most probably the behaviour would be just the same.