How to change description on AWS Security Group with Terraform

I'm having a bit of a trouble with the following Terraform scenario:

• create a SG and launch an instance that uses the SG
• modify the SG description

I would expect Terraform to unlink the SG from the instance, destroy the SG, create a new one, link the new one.

However, what I'm seeing is a timeout while trying to destroy the SG (obviously, as it's in use and AWS won't allow that).

I'm not sure whether this is a bug or I'm doing something wrong.

To understand my issue, as per below run apply, then change the description of the SG and then run apply again.

provider "aws" {
  region = "eu-west-1"
}

resource "aws_default_vpc" "default" {
  tags {
    Name = "Default VPC"
  }
}

data "aws_subnet_ids" "example" {
  vpc_id = "${aws_default_vpc.default.id}"
}

resource "aws_security_group" "webserver" {
    name = "staging-webserver"
  description = "meow"

    egress {
        from_port = 0
    to_port = 0
        protocol = "-1"
        cidr_blocks = ["0.0.0.0/0"]
    }

  tags {
    Name = "EBS webserver SG - staging"
  }
}

resource "aws_instance" "dummy" {
  ami               = "ami-f7e8558e"
  instance_type     = "t2.micro"
  availability_zone = "eu-west-1a"
  vpc_security_group_ids = [
    "${aws_security_group.webserver.id}"
  ]
}