The bug

The following is based on a decompiled version of Minecraft 1.9 using MCP 9.24 beta.

The method net.minecraft.block.state.BlockStateContainer.StateImplementation.withProperty(IProperty<T>, V) throws an IllegalArgumentException if a invalid value for a property is given. This is problematic because there are multiple situations in which the user can directly provide a value.

I would instead expect it to ignore this property but print a error message in the log.

How to reproduce

1. Use the following superflat preset

   3;minecraft:hopper:1;1;
   

The game will crash because the value "1" is invalid as facing value (it would be "up")