Domain class with ID that is using UUID generation does not work with @Mock in service class

Given a domain class that has an ID with UUID generation turned on:

class MyDomain {
  String id
  String desc
  static mapping = {
    id generator: 'uuid'
  }
}

When I attempt to mock multiple instances of the domain class:

new MyDomain(desc: "One").save(flush: true)
new MyDomain(desc: "Two").save(flush: true)
new MyDomain(desc: "Three").save(flush: true)
new MyDomain(desc: "Four").save(flush: true)

Then when I attempt see the count of domain objects in test I see:

assert MyDomain.count() == 4

with result: 1 and failed assertion.

Then I check on each domain object to see what is it's ID and all of them have an ID of 1 after creation. It seems that the domain objects that are created do not have an appropriate generated ID and instead try to update the first domain object created. When I look at the 'desc' attribute after saving all 4 of them:

assert MyDomain.findAll().get(0).desc == "One"

The result is that the 'desc' attribute actually equals "Four", the last value to be saved.

The expected behavior is that I save 4 instances of MyDomain and that each has its own ID value even when UUID generation is turned on in the MyDomain mapping.