I've seent he 'flying Keris' videos on youtube, but they all look either proped-up against the scabbards, stuck into wood surfaces or faked hung on a wire.
I've never had a knife, dagger or sword that would stand on it's tip.
As for the Jambiya
I have noticed this before with steeply curved blades.
It reminds me of the old 'balance toys' that used to be popular, even the chrome wire 'executive desk toys' of the 1970s.
I've had several curved swords that would balance in this way.
It looks cool but when you think about it, it's logical that they would balance and it's like the old trick of the two forks and a coin, How about two forks balanced on Sitas fingertips?