Taliyah ultimate misses on very quick double R cast (possible bug; not sure)

As Taliyah, I often double cast R since I planned to use it as a movement ability. There appears to be a narrow window after the R1 cast where the game will ignore an R2 cast. On my old keyboard, I can hit this supposed window ~1/10 casts at best. On my new keyboard, I can hit the window ~7/10 times. In the past (playing on laptop keyboards and a fairly basic desktop keyboard), I can land a R1/R2 super reliably with just the double tap. If I miss the double tap, I'd figured it was on the outer edge that I missed the end of the "ride" window (I'm not super good at this game).

A week or so ago I got a new mech keyboard (Razer Huntsman), and now I have a lot of issues hitting the double cast. At first I thought this might have been a PBE bug, but I can reproduce it on live. Unfortunately, in the "what changed" question IT/programming is famous for: both my patch and keyboard changed so I can't say whether this was an issue before 9.9.

From autohotkey (which I use to swap the control and capslock keys for ergonomics), I can see that both R taps are registered even if the R1/R2 ulti is missed. I did a bit of number crunching from the recorded time deltas from AHK and I figure that the time delta roughly between 0.00 seconds (unmeasurable by AHK's resolution) and 0.05 seconds between the R1 key-up and R2 key-down is the magic area where the game engine can miss a key, tested using my old keyboard (Tesoro low profile blue-ish switch), the new Razer, plus two membrane keyboards. I was mildly surprised to find that on one of the membrane keyboards (and a wireless one to boot) it was almost as easy to hit the R2-fail window as the wired Razer.

and yes, before anyone asks, I did try this with all third-party background apps off.

So I'm at the point now where I think this is a bug, but I'm not sure how to test it further since I don't know of anything else off-hand that buffers the way this does.

I'm happy to test other champs or situations on my setup.

System info:

• WIndows 10 1903 (19H1) build 18362.53 insider preview
• Core i7-8700k @ 3.70GHz
• 16GB RAM
• GTX 1060 6GB
• no over/under clocks