The bug

Even though the data command requires operator privileges it is only logged on the client side. The old /entitydata command was logged on the server side and /data merge is too.

How to reproduce

First enable logging:

• /gamerule logAdminCommands true

• /gamerule sendCommandFeedback true

  Then run:

  /data get entity @e[limit=1,type=skeleton] Pos

  and

  /data merge entity @e[limit=1,type=skeleton] {a:b}

  In the log file you'll now see that the /data get command was only logged on the client side and not on the server side:

  [23:42:42] [Client thread/INFO]: [CHAT] Skeleton has the following entity data: [-67.49344557655863d, 49.0d, 91.34854618916114d]
  [23:42:44] [Server thread/INFO]: [Adrodoc55: Modified entity data of Skeleton]
  [23:42:44] [Client thread/INFO]: [CHAT] Modified entity data of Skeleton

This is a problem for me because now there does not seem to be a way of writing any NBT to the server log. This was very useful, because the server file could be read by an external program to get commands from Minecraft with this library: https://github.com/Energyxxer/Vanilla-Injection

Note that the client side log message of /data get is not generated when using command blocks.