GroupWise client deletes attachments that have the name of a registered mimetype

If you create a text document named TEXT.CALENDAR and another called text.calendar, and put anything in those documents, then drag them to the attachment window, as soon as you click on send the both disappear.  However the one with the lower case name does get delivered

The workaround is to use lower case if the file must have this name.  Otherwise use a different file name.