CommentThreads amount changes by order - youtube-api

Question

CommentThreads amount changes by order
Hi I'm trying to fetch all comments of a video. For testing purpose I'm using this video Id U55NGD9Jm7M.
When I order by time I get 1538 comments the last wrote on the 02.05.2015.
If I’m using the relevance I only receive 1353 comment and the last was wrote on the 29.04.2015
This doesn’t seem right to me. I expected to receive the same comments but in a different order and not different comments.
I also tried this on a different video and the results were the same.
My code cut down to minimum
Thank you for your help
public class foo
{
public void bar(string videoId)
{
var allTopLevelComments = new List<CommentThread>();
var searchListResponse = getThread(videoId);
allTopLevelComments.AddRange(searchListResponse.Items);
string nextPage = searchListResponse.NextPageToken;
while (!String.IsNullOrEmpty(nextPage))
{
searchListResponse = getThread(videoId, searchListResponse.NextPageToken);
nextPage = searchListResponse.NextPageToken;
allTopLevelComments.AddRange(searchListResponse.Items);
}
var first = allTopLevelComments.OrderBy(c => c.Snippet.TopLevelComment.Snippet.PublishedAt).First();
}
private CommentThreadListResponse getThread(string videoId, string nextPageToken = "")
{
var youtubeService = new YouTubeService(new BaseClientService.Initializer
{
ApiKey = "my key",
ApplicationName = "my app"
});
var searchListRequest = youtubeService.CommentThreads.List("id, replies, snippet");
searchListRequest.VideoId = videoId;
searchListRequest.MaxResults = 100;
searchListRequest.Order = CommentThreadsResource.ListRequest.OrderEnum.Time;
searchListRequest.TextFormat = CommentThreadsResource.ListRequest.TextFormatEnum.PlainText;
if (!String.IsNullOrEmpty(nextPageToken))
{
searchListRequest.PageToken = nextPageToken;
}
return searchListRequest.Execute();
}
}