Created Unassigned: Errors while searching [1854]

Hi I'm getting error for searching when I change fetch mode to anything other than header/none

Message[] msgs = _client.Folders.All.Search("unseen", ImapX.Enums.MessageFetchMode.Tiny, 10);

This line generate following exception -

{System.Collections.Generic.KeyNotFoundException: The given key was not present in the dictionary.
at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
at System.Net.Mime.ContentDisposition.get_FileName()
at ImapX.Parsing.BodyStructureParser.ParsePart(Int32 number, Int32 level)
at ImapX.Parsing.BodyStructureParser.Parse(Int32 level)
at ImapX.Parsing.BodyStructureParser.Parse(Int32 level)
at ImapX.Message.TryProcessBodyStructure(String data)
at ImapX.Message.ProcessCommandResult(String data)
at ImapX.ImapBase.SendAndReceive(String command, IList`1& data, CommandProcessor processor, Encoding encoding)
at ImapX.Message.Download(MessageFetchMode mode, Boolean reloadHeaders)
at ImapX.Folder.Fetch(IEnumerable`1 uIds, MessageFetchMode mode)
at ImapX.Folder.Search(String query, MessageFetchMode mode, Int32 count)