markets don't match

Until recently, I used the 'old' BF site on an old version of IE with the original Gruss refresh scripts using "classic" view, I think it was called. If you ran this alongside the 'old' site on a newer browser then the amounts in the markets differed considerably, most noticeably on the football markets, it could be 10's of K different.
My theory was that since using the best price practice, cross matching bots and all that other carp the amounts fluctuated, but were not represented in real money, for whatever reason, in the newer setup. The older setup seemed to represent the actual ammount of 'real' cash in there.
I know it doesn't really answer your question but gives an indication of how the amounts to back and lay can be deceiving

virtual/XM offers, looking to trade a guaranteed % profit through the market.

These bets then "float" as the market moves.