Riven R bug

Since 6.1 came out I noticed that leveling up the ultimate while having it active (so, still with wind slash' icon) puts it at the cooldown it had before leveling it.

This never happened before, I'm not really sure that it's a bug but well, since Riven's R goes on cooldown after the 15s duration and not when casted, it should be.

Quite randomly this can be seen in this video https://m.youtube.com/watch?v=39AokVJuMgs As you can see, his ult goes on cd for 53 seconds, while the cooldown at level 3 is 33s (all with 45% cdr, clearly).

Usually isn't THAT gamechanging, but who knows.