It's OK if you read it as 'the people (who have) sat behind them'.
Past participle, innit.
(
_Felix 's school of dance and occult sciences,
Tue 19 Jul 2011, 17:08,
archived)
Wouldn't he have had to put (felt) instead of (feel) to make it past participle though?
And shouldn't it have been (that were) and not (Who have)not that I know, I'm just typing rubbish to fill five minutes....
(
The invisable man Is having a long lazy soak in search,
Tue 19 Jul 2011, 17:24,
archived)