Yeah this bug is still present in the game and occurs with any channels, including Yamato's power slash. I'm able to very easily replicate it in sandbox. It has to do with the amount of distance traveled with Flying Strike, short range FS do not trigger the bug.
Demonstrated in sandbox but can be replicated in any normal match. Upon using Power Slash immediately after landing from a long distance Flying Strike, the channel starts but is instantly interrupted and needs to be restarted again, instead of getting a "You Are Busy" prompt. This does NOT...