Bukkit

What steps will reproduce the problem?
1.Implementing the iron_bars, and stone_slab in the config at barrier like sayed: - IRON_BARS   (below)  - STONE_SLAB
2.reloading and even restarting
3.Driving over the items.

What is the expected output? What do you see instead?
Instead of been blocked by it like the fence i ride/jump over it.
I can't add any item. I even tried the id's

What version of the product are you using?
uCars v19.5 for Spigot 1.8.6

Do you have an error log of what happened?
No, it doesn't output a error log at that moment

Please provide any additional information below.