Lux Team Ult Inidicator - Final Spark Bug

So I had been playing with lux as a main for a few months and multiple times I try to cast final spark (R) for lux and then would be killed before it would go off. When this happened everyone would see that I had used my ult. Myself, on the other hand, did not and could still use it on respawn and in many instances, I would just to prove I still had the ability to do it to my teammates who argued and said I did not because the indicator said otherwise. I noticed this actually happens a lot. I am not sure if others experience this but I thought it was a kinda interesting bug. Just a note it wouldn't happen every time. it was when I was literally about to cast it but nothing happened.