Upon making the background of a gnome-terminal "transparent", the entire system becomes very jerky and belabored, any text reported in the gnome-terminal window itself or any repainting thereof is especially so. CPU resources are completely overtaken by the gnome-terminal process during any activity of the terminal.
Created attachment 29980 [details] emerge info
This seems to be the same problem of bug #31830. Please try emerging vte-0.11.10-r1 and see if that resolves it for you.
In my case that seems to be it, thanks. I updated from x11-libs/vte-0.11.10 to x11-libs/vte-0.11.10-r1.