I believe I found a bug when using MapiAttachment.Save(Stream stream) on an OLE attachment (attachment with PR_ATTACH_METHOD == ATTACH_OLE).
On the message I was testing with, I noticed that using MAPI to download the O…...download the OLE attachment I got a file with a size of 1,108,992 bytes...save the attachment, I got a file with a size of 1,098,214 bytes...