I have had no issues while travelling on staff travel either. Especially now with online standby check-in and all that, most of the time you won't have the need to visit the staff travel "shed" and staring at screen waiting for the green signal like an F1 driver.
There was even a time when I got a free upgrade to J class at COK, even though I was travelling on a Firm Y class ticket. And I work at a lower grade that never gets to travel J/F class.