I have been trying to find the approximate cause of the bug. If you hold talk, while holding F while at the same time failing the skill check once it passes the white line, it will glitch the skill check and as long as you continue to hold F it doesn't matter if your partner fails you will get the skill check for free. I've been able to replicate it many times but can't find the exact cause. But I noticed it frequently happens when you use voice, hold f and fail the skill check. The mods will figure it out :)