I received an email message with a text attachment that contained a MIME-encoded email that included the user's public certificate. The file was named smime.txt. Stuffit Expander 11.0 tells me that there is nothing compressed or encoded in the file. Stuffit Expander 10.0, on the other hand, created a folder containing the certificate and the message content.
It turns out that in Stuffit Expander 11.0, I had to change the file extension of the attachment from .txt to .mime. Once changed, Stuffit Expander 11.0 presented the same result as Stuffit Expander 10.0 had without the bother. I have Stuffit Expander 11.0 on a MacBook Pro, and Stuffit Expander 10.0 on my PowerPC Dual G5 desktop. I wouldn't think that would have made a difference, but could be.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20061121134216208