With kernel 3.13 and nVidia driver verison 331.49 I have the following issue: when I switch to a console with ctrl-alt-f1 I only get a blank / black screen, no command prompt, no nothing.
I only can switch back to KDE with alt-f7.
It does not happen with kernel 3.11. Using kernel 3.11 I can switch to a console and get a normal command prompt.