First program line corrupted after OLD command

[RoelandR]

When I load a BAS program it runs fine
after the NEW command I type some commands with or without errors
after that I type OLD to restore the last program
Then the first line is corrupted with the last command line I typed

[stevesims]

Whilst I have also observed OLD not restoring correctly, for me the failure only ever occurs if I have entered a statement that has caused an error of some kind.

Typically I get caught out by this on rebooting my Agon. I'll mess up typing OLD, because the Agon reboots without caps-lock enabled.