My question is that, has IB changed its policy? If so, when this started? I know the current status now.
Your question was already answered in the third post of this thread, by @eastern_warrior. Obviuosly you did not read it.
Anyone can read post #3 that does not answer my question. We do not need any lawyer to understand it. If you do not get anything else to say, just let it to be.
As Bone mentions, the policy change is due to the possibility and new reality that the contract can have a negative settlement price which means the downside loss isn't capped and thus the possibility of large losses in an illiquid contract can not be capped. This was implemented shortly after the negative settlement of the contract in May. I'm fairly certain notifications were sent out to clients.
Was this change on all financially settled commodity contracts? Like QG MCL and others? Hope you do realize that those financially settled contracts do expire earlier phy. contracts. Also extreme prices can happen over other periods than settlement day. It seems IB likes to over-react to make those changes.
The statement is pretty clear - all oil futures. Extreme prices can happen at other times but the combination of lack of liquidity and large moves without a chance to manage is a factor. I do not believe we are the only firm implementing such restrictions.