Unfortunately, IB doesn't handle fungible contracts well.
Intraday, you will find that your account equity may vary widely, because it values the two "sides" of your flat position differently, based on the current bid/ask and or last price of each market. If one or both of the contracts are illiquid, these valuations can be quite different from one other, resulting in a significant change to your real-time equity display. This can be kind of scary, and generally requires you to keep some extra "breathing room" in your account to be safe. Nightly mark-to-markets on the statements are almost always correct, valuing them both at whatever the clearinghouse determined for that day (unless there is a problem with the feed, which happens rarely).
Also, it doesn't exactly follow SPAN, in that it does take some margin (performance bond) for the position. For a +2xE7/-1x6E position, this is $200 initial/$150 maint. According to the CME website, there is supposed to be $0 requirement for this position.
I've carried a GE/YE spread into final settlement, and it was correctly settled, closing both contracts at the same correct price. I'll note that I was charged commission on those contracts to settle them.
With physically settled contracts (like 6E/E7 Euro FX), however, you basically need to unwind your positions before the first notification day (final-3 in this case) or risk IB liquidating you. Theoretically, this shouldn't be necessary, since the clearinghouse knows that your contracts are equivalent, and it has no affect on the firm's outstanding positions, but apparently IB's system wouldn't know that when it gets the net position from the clearinghouse and allocates them to the open contracts in customer accounts.
I beat this subject to death some time ago, but couldn't get it resolved. Management cited more important matters as the reason.
After this Euro run, I'm wishing that I didn't have the short side of my current flat position
OT: Did anyone else see the blurb on the website scrolling news ticker "IB Cuts Euro Futures Commissions to 2.00 Euros"? I can't find any other mention of it. I wonder which futures it applies to. This is even cheaper than their Globex commish!
