Still testing this trigger ..................
£1.00 BACK bet fired-in at 4.5 odds; bet MATCHED 2 seconds later; £1.05 LAY bet fired-in at 4.3 odds 1 second later; PARTLY MATCHED (15p) 16 seconds later but the LAY Bet Ref. did not show the LAY bet as being PARTLY MATCHED i.e. it wasn't suffixed with a 'P'.
"If a bet is partially matched and the unmatched portion has not been cancelled then the bet reference will have P as the suffix (eg. 3230882684P)."
Result: 90p of the LAY bet not MATCHED for a successful trade.

Any ideas??