answer this at your leisure (ha ha)...
the Doctor Who story The
Leisure Hive, the Doctor and Romana comment
on a recording that supposedly shows a time experiment. They
realise that the experiment has been faked. However, the tape
has stopped playing before they enter the room. Not
only that, but all the other characters in the story also
behave as though the Doctor and Romana have seen the recording.
plot hole can be remedied if we simply assume that the tape
is on a loop and starts playing again after the end of the
recording (though on mute, since we don't hear it). Rather
conveniently, we cannot see what is happening on the monitor
screen as the Doctor and Romana enter the room, so there's
nothing to contradict this theory.
given the presence of Nigel Lambert as the scientist Hardin,
perhaps The Leisure Hive isn't a Doctor Who
story at all, but a futuristic episode of the spoof science