I'ts a mod that lets you place "Jump Vader" blocks similar to the Quark mod's elevators. You simply place one above the other at any vertical distance, and jump/crouch on top of the block to go in between the different heights.
If you've spotted a bug and want to DISABLE the JumpVader's, please do so via the config file in your servers Config folder. Otherwise, just stop the server, delete the mod from the mods folder, and start the server back up.
NOTE: Removing the mods from the mods folder will delete all JumpVader blocks in inventories and the world permanently!