I was going to make a video of this awhile back actually, though never did since I was trying to figure out who can do it besides Pai. @Wazaaaaa Codemaster made a video with Pai for this back on Ultimate lol.
My god that is so fucking dirty bro nice video. This happens because the "Switch Frame (forward/back-turned)" is 1F for those moves. Jann Lee has something similar with his P+K (turns him BT on frame 1).
The backturned mechanic is pretty flawed in every DOA, they should just give everyone the ability to block instantly from BT (and from standing to crouching too), it would solve so many issues.