/tag not working with non-OPs

You cannot have a player step on a pressure plate to remove their tags. They must be OP for tags to be removed, even if a command block does it for them. This is the command: 

/execute @p ~~~ tag @s remove TAGNAME

 

This doesn't make sense, considering they can be executed and enchanted while not being OP.

This is the command that works:
/enchant @p unbreaking 3