I have not seen this effect on my FXCM accounts, but they had mostly been overcapitalized - even the Z5 account had still capital after the margin call. I know that another one of our developers also had only one of his FXCM accounts affected.

It depends on your contract. Contracts are usually per client, not per account, so it definitely makes sense to open accounts with different brokers. Still, different accounts can only be affected when the contracts allows that you're charged for a negative balance.

Currently it looks as if FXCM had survived that mishap.