A non-operator player cannot use all commands with op permission level 0.
- Try as a non-op to use one of the affected commands
- Op yourself
- Stop the server
- Open the ops.json file and change the level value of your entry to 0
- Start the server
- Try to use one of the affected commands
→ Despite the fact that the affected command requires op level 0, which in theory everyone has, you are unable to use it if you are not an op
The following is based on a decompiled version of Minecraft 1.9 using MCP 9.24 beta.
The reason for this is that the method net.minecraft.entity.player.EntityPlayerMP.canCommandSenderUseCommand(int, String) explicitly tests if the command is either "tell", "help", "me" or "trigger". Instead it would make sense to test if the required permission level is 0 or less.