Screen Saver Not Working In Clamshell Mode

I have an external monitor so I utilize Clamshell Mode from time to time. When my MacBook is open (as a second display) and plugged into my external monitor the screen saver works. However, when in clamshell mode (Macbook screen closed) the screen saver never engages. I currently have my screen saver to start at 10 minutes. I do use an after market screen saver. I thought this was the problem at first, but this occurs with the stock screen savers too. Anyone else experience this? Anyone have a way to fix it?

Thanks!