Edited Unassigned: MessageCollection.Download() crash [1911]

When trying to download a specific email with anything more than just the headers, using

folder.Messages.Download(new long[] { uId });

the app crashes:

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(Int64[] uIds, MessageFetchMode mode)
at ImapX.Collections.MessageCollection.Download(Int64[] uIds, MessageFetchMode mode)
at XXX

The specific email is an old (Mar 2012) store receipt from the Apple store.