Domain validation errors should not replace any previously existing errors

Currently, when you run a domain's validate() or save() method, any previously existing errors in the domain's errors object is replaced. For instance:

domain class TestDomain

def test = new TestDomain(params)
test.errors.reject('custom.error.code')
if (!test.save()) {
println test.errors
}

The println will only show validation errors caused by the save() method. The previously added error message is now gone. This SHOULD NOT be the intended behavior.