I can't say anything about "flashes screen". But:
ubuntu 14.04, 64 bit, nvidia (331.38) and bumblebee (3.2.1-90)
before using optirun, "optirun --status": Bumblebee status: Ready (3.2.1). X inactive. Discrete video card is off.
After using optirun, "optirun --status": Bumblebee status: Error (3.2.1): [XORG] (EE) Server terminated successfully (0). Closing log file.
Problem can be solved by 'sudo service bumblebeed restart'.
I can't say anything about "flashes screen".
But:
ubuntu 14.04, 64 bit,
nvidia (331.38) and bumblebee (3.2.1-90)
before using optirun,
"optirun --status":
Bumblebee status: Ready (3.2.1). X inactive. Discrete video card is off.
After using optirun,
"optirun --status":
Bumblebee status: Error (3.2.1): [XORG] (EE) Server terminated successfully (0). Closing log file.
Problem can be solved by 'sudo service bumblebeed restart'.