Dear AWS Customer,

When you restore a snapshot to a new RDS instance, then you get a radio button option to select "Multi-AZ" deployment option, the instance is then restored accordingly and this is an ideal behaviour.

I can confirm that it is a known bug in the RDS console and currently being investigated internally. Currently, we don't have an ETA on it. The workaround is to utilize the AWS CLI in the meantime for restoring.

I apologise for the inconvenience caused due to this issue.

I hope above information helps. However, if you have any questions or concerns related to this issue please keep an eye out on your support case.

References:

Restoring from a snapshot: [+]https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_RestoreFromSnapshot.html#USER_RestoreFromSnapshot.Restoring