That is where I am confused, as I thought that a FULL backup which does not perform a Tlog backup as such, does affect the transactions so there is no tlog backup file to copy and the next tlog backup at 07:00 will only have transactions since the full backup and not since the last tlog backup at 21:00.

I guess within log shipping it is intelligent enough to identify transactions in the full backup to copy without a normal tlog bak file.