When you enable the Not the selected attachment types option under the Attachment True File Type filter, VSAPI cannot determine the real file type of the attachments. Thus, the attachments are deleted.
Hot Fix Build 14510 allows you to add more filename extensions to the list of true file types that VSAPI can detect.
Release date: May 5, 2011
Trend Micro recommends applying patches or service packs instead of individual hot fixes whenever possible.