Interactive brokers -- need some assistance please

I've recently started using this platform, and have already rolled two contracts from one period to the next, in gold and in soybeans, using "combinations" and it was very easy.

I'm attempting to do the same in EUR/USD, but the "combination" price doesn't seem to deal. I've spoken to IB about this and they tell me the best way to roll is by legging it, i.e. don't use the combination as it's non-guaranteed.

Anyone know anything about this?