Thanks Bill (& Dave)
I realised this was expected behaviour, as you say 3 periods then moved into what I called "no mans land" .
Good to know that if propagation or QRM allowed it would probably have completed even though I successfully chose to start fresh above 1000Hz.
What I didn't expect was that there appeared to be no time out on my subsequent transmissions while I was sending the report. - For the record how long would I have continued to transmit his report - is this set by the usual Tx timer that is set for "normal" FT8 mode or would it have continued forever until I decided to give up?