Some RCON command doesn't work anymore (incorrect argument)

Some RCON command doesn't work anymore.

For example when the command list is sent to the server, it reply :

Incorrect argument for commandlist <–[HERE]

Same for the op player command :

Incorrect argument for commandop player <--[HERE]

These commands worked for a connected operator on the server, or through the stdin.

For the command help, it not work alone but with argument it work :

help op return :

/op <targets>

So strange behavior for RCON.