I had a quick look at the T&C and my interpretation is that if they suspend trading as they did they will either close bets at current value or void trades. Either way according to thier own T&C they shouldnt have let the trade continue so without doubt they were in the wrong.
Question is (as someone else pointed out) they would have also had customers on the other side of the trade, what did
IG do about those trades? My thinking is they would have voided the trade straight away but it would be interesting to know.
It just proves the point that like most compainies (not just SB firms) IG will happily try it on if they think they can get away with it. The fact they settled so fast IMO does not reflect well on them as it adds weight to the argument that they knew they were in the wrong but tried it on anyway.