if i try to use § or the l3 letters on the chat or/and command block, the §, will disappears and all the text in front of him too.
(when you try to re-write the disappered text, the command will disappear...)

this is what i was trying to do
w @p §6@p §0welcome

then it disappears
w @p

and in the end when i retry all the command will disappear