I recently bought a spastic arrow and it didn't work with my infinity bow, regular arrows work but not these, they used to though. I then tried with all the new cool arrows. Is this a bug?

 

They're not meant to from what I've heard. When the arrows were first implemented, they were too OP for infinity so Tanner(the DEV) changed it so infinity doesn't work for these arrows.

Hope this helped.

 

Yes, crew asked me to make sure special arrows defy infinity enchantments. This is not a bug, just a way to level the playing field. You can still use normal arrows with infinity, however.