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The /reload command is only available to opped players in singleplayer and multiplayer.
So are /stop, /kick, /ban, etc. in multiplayer.
Although when inserting "/r" and "Tab" a couple of times, the list will suggest /reload.
Likewise with "/s", "/k", "/s", etc.
This happens because the same list of commands available for an opped player is used in the command block as well.
What should happen: All commands that the command block has no permission to, need not to be suggested using tab completion.
This can be achieved by only showing commands for players with op-level=2
(because any regular commands are shown to players with this op-level correctly)
This may confuse newer players why those commands would not work in a command block, because clearly they are suggested. (And the error message might need some attention too: "This command can not be run by command blocks")