Its all about professional level flying and situational awareness. The Pros know what (and and what NOT) to expect from their instruments and how to deal with it. If you're not aware of the potential for glide slope errors, and that your on board automation may not act properly, they you're just not up to standard. Another way to look at it might be, when on final approach, if ANYTHING does not look quite right, get out of there - and figure it out at a safe altitude. I think it is called a GO AROUND. You certainly can demand a do-over, but its smart to claim it before you're over the numbers. Duh? If one is flying at the commercial level, I would hope that you already know this stuff and that you're thinking is generally along the same lines. Being faced with a surprise when crossing the numbers - whatever the situation - is not professional level situational awareness.
