As you can clearly see from the video, there is an unusually long time between when I press the button and when it releases. This problem also applies to things like pressure plates. ThrownPotion entities incorrectly display as a splash Awkward Potion (or any blue base potion) and break shortly after hitting the ground.
Ignore the bit at the end of the video.
What is happening in the server console? Do you have a lot commands running?