I had a similar experience at a park here in Australia. I don't have it on film though, because I never record my hunts.
I got a faint signal jumping between 12:36 - 12:40 on the CTX (said about 18cm/7in which isn't too deep). From past experience these type of signals can indicate a deep penny (which appears shallow on the detector) so I dug a deep plug, and dug down about 20cm (7.9in). Pinpointer doesn't go off yet, so I dig down another 10cm (4in), and it still doesn't. So I dig a final 10cm (4in) down and the pinpointer is still silent.
So I put all the dirt and the grass back, and go over the spot with the detector. I only get an iron signal (33:46 etc) where the previous good signal was. I flip the plug back over and scrape some soil away, and down at the bottom of the hole (about 25/30cm) I see the outline of a small silver coin (on its side). It was a thin 1901 English Threepence (they're small, only 16mm (0.6in) in diameter.
I think what happened there is that coin was much shallower when I originally picked it up, and I must've scooped it out the hole with the dirt. But whatever the case, if it had been that deep to begin with (only giving off the iron signal), I probably wouldn't have dug it.