In the past 24 hours in the sabayon irc channel, I saw more than one person bring up this problem, so I'll post it here. Both scenarios are similar, and quite odd.
Person is running sabayon in a virtual environment (unsure if it was vmware or virtualbox). Under the VM, when the spritz window wasn't in focus, it would pause.
Person decided to do a world update using spritz. Figured it would take a while, so he went about his business doing non-computer things. When the screensaver came on, it also paused spritz. Person comes back to computer several days later, and it's still on package 24 out of 96 packages.
What is making spritz pause indefinitely in these situations?