Managed to successfully put the blocks together in Creative, got into a dungeon. Found a dispenser with an oak button next to it in a room full of beds. Right clicked the button. Crashed with this error:

The game crashed whilst unexpected error
Error: java.lang.ClassCastException: net.minecraft.client.world.ClientWorld cannot be cast to net.minecraft.world.server.ServerWorld
Exit Code: -1

Successfully able to replicate it upon reloading the world.

I can't replicate this. Are you playing single player or on a server?

There's also nothing modded here. It's just a vanilla dispenser, containing 3 ordinary lingering potions of Healing II, with an oak button. If you build that setup in the Overworld does that crash too?

Single player, but it crashes outside the dimension when making the same contraption. I'll keep testing to see what might be making redstone unhappy.