Double tapping (d-tapping / 2-tapping) someone with blast protection 4 armor using end crystals makes them fall down a lot faster than they should be.
What is d-tap? A d-tap is a technique used in end crystal PvP to quickly kill someone holding a totem of undying. When you hit someone with a sword their body goes red (called damage tick). You then combine the damage from you sword with 1 end crystal within the same damage tick. After their damage tick ends you crystal them again which will kill them.
Here's a video of the bug: https://youtu.be/MG2UHmturvM
Here's a video which explains more about d-taps / 2-taps https://www.youtube.com/watch?v=4LN5Uf7KHW0
They should fall down slightly slower if they get d-tapped than if they get hit with 1 crystal.
They fall down way too fast if you d-tap them.