Based on 1.11.2 decompiled using MCP 9.35 rc1
Data parameters are used to detect changes and send them to the client. However, the POWERED data parameter is also set by the client which kind of defeats the purpose of the parameter.
Based on MC-112988
- Place a furnace minecart and power it
- Reload the world
→ You will see that it appears as unpowered. This happens because caused by MC-112988 the fuel value is 0 for the client. The server is sending the correct POWERED data parameter value but the client is overriding it.