Betfair - bot mischief ?


I placed a bet today on Betfair's exchange on Southampton to beat Man U.There was around £90 available at 2.64,and £104 at 2.62.I bet £194 at 2.62 - expecting to get a mixture of 2.62 and 2.64.
But I actually got under 2.621.I'll be more careful next time,and place the bets separately.I suspect some monkey business by some betting 'bots.