This issue happens in Parser.parseLro(): if only shortname is provided, and has ambiguity with message types from other protos, the parser currently naively matches on first encountered type, without throwing exception or indicating conflict.

Example proto to reproduce:

• Annotation type is ambiguous with DescriptorProtos.GeneratedCodeInfo.Annotation
• Location type is ambiguous with DescriptorProtos.SourceCodeInfo.Location

service TestService {
 ...
  rpc annotationTest(Request) returns (google.longrunning.Operation) {
    option (google.longrunning.operation_info) = {
      response_type: "Annotation" 
      metadata_type: "Location"
    };
  }
}

message Annotation {
  string name = 1;
}

message Location {
  string name = 1;
}