Back in the early 70's, the telegram service was automated. To tell the computer that the end of message had been reached four N's (NNNN) was sent.
This was OK until someone sent lower case N four times (,,,,) in part of the telegram which was the same code as N. The difference being the lower shift code was sent prior to the ,,,,.
To overcome the problem, all operators connected to the system were instructed to put the lower case code in between the ,,,, which would not show up on the telegram and stopped the message ending prematurely.
It is often the simple things that catch you out.