Running out of swap space with 8GB ram [possible bug]

I don't know why this happened, so I think this might be a bug in FreeBSD 10.3-p11. For some reason my server ran out of swap space while updating ports that where compiling, this resulted in a freeze and I had to hard reboot the computer. It seems that swamp is not cleaned of old items and over a long period or heavy that resulted filled up swamp area (around 10GB in size).

I don't know why the FreeBSD did freeze, this computer has 8GB of ram installed.
wonder about build dependency loop ... else you could have some other daemon running and eating memory, in which case should not be too hard to identify which one ...
There seems to have been some loop going on after the cold restart (rebuilding perl), I'm not sure about before. Can't rule it out however. I restarted the rebuilding process by running this command to fix dependency issues with OpenSSH.

portmaster -f `pkg shlib -qR`

This seems to be working without problem at the moment. What I have left is to rebuild perl (upgrade to 5.2.24) and the packages connected to it.