I've been on betfair all morning, no problems.
Regarding your scenario, I wouldn't place 5 bets on 1 betslip and then try and lay them, I would do them one at a time so there's less to go wrong.
Also before you start you should have betfair and the bookie open so unless your connection went down at the precise moment you wanted to lay you bets it wouldn't be an issue, but point taken there is some risk
"All you need to ask yourself is do you feel lucky? Well do you......Punk!"