Ted,
Photo Mechanic Version 5.0, build 15800 (e6ecc1c)
Mac OSX 10.8.5
I tried to reproduce your problem and was unable to get a contact sheet showing no files in it.
Here is what I did, please tell me if I have done anything wrong:
1) Created a folder called "Space at the end "
2) Put a JPEG in it.
3) In PM, I chose "Open Contact Sheet..." from the File menu.
4) Navigated with the folder picker dialog to the "Space at the end " folder and chose it.
PM opened the folder as a contact sheet tab and showed the JPEG that I had earlier copied there. I'm on Mac OS X 10.9.5, by the way.
-Kirk