Difference between market in play and settled p@l

What i see is that my potential profit in the in play market (the green number) is then reduced when the market is settled. Previously this number always used to be very accurate (or out by a penny or so on settlement) now there is a big difference in pounds and always reduced.
I've recently upgraded and this never used to be the case.
Is this a bug or is it a setting I need to check?
Cheers

hi
in the general options tick the 
Show P/L net of exchange commission  (on the right middle of mfp screen)


mcbee