The company I fly for had a false GS capture, which according to the flightsafety departement and the manufacturer of the airplane was a 9 degree GS in reverse sensing.
The pilot flying totally lost SA and started descending fully configured and at final speed to pick up the GS from above (was a little high, but not disastrous). Due to being overloaded (still in line training) he descended with less than 3 degrees, so not enough to follow the GS, let alone pick it up from above.
The instructor saw it, gave hints, but decided to let the trainee go on for a while to show his error. In the instructors mind a go around was already decided upon and just before he wanted to call it, the aircraft intercepted the 9 degree GS, which resulted in the plane trying to follow it upwards, so it started to climb with 9 degrees.
Needless to say the autothrust had problems keeping up and a certain shaking sound was heard for a split second before they could take over.
What we have been told after investigation is that the 6 degree path would produce a flag in the cockpit but the 3 degrees (obviously) and 9 degrees are there, with the 9 degree in reverse sensing.