switching to vt causes a freeze

[David S]

dear list,

recently, when i'm compiling my -current box to the latest sources, i am 
greeting with this sight: https://i.imgur.com/QUG4AMr.jpg

it happens after i type in "shutdown now". in preperation to do a "make 
installworld".

this can be migitated by shuting down X prior to the operation (for 
example "service gdm stop").

no idea what is causing this, i'm running the propietary nvidia blob driver.

greetings,
david s