Actually, OptiFine developer fixed this bug -> GitHub issue
@conem I honestly just behaved like others here, didn't mean to break any rules or something.
Reproduced in 1.16-pre8
I was able to reproduce this bug in Minecraft 1.16-pre2
Was able to reproduce on 20w17a
Still reproduceable in 20w11a
Still able to reproduce in 1.15.1
Also still able to reproduce in 1.15.1-pre1
Still able to reproduce in 1.15
Reproducible in snapshot-19w46b
Still able to reproduce in release 1.14.4
Still able to reproduce in 1.14.4-pre6
Still able to reproduce in 1.14.4-pre5
Still can reproduce in 1.14.4-pre4
I have just tested it on 1.14.4-pre3 — this issue is still thing there.
P.S. Yes, the comment above was made also by me, but I literally forgot that I already had an account on this site 😃
In 1.12.2 animation of cape more smoother, than in 18w11a
The bug is present in 1.18-pre5.