If you right-click in the dialog, what types of files do you have selected?
At first I see the standard message box with "No more differences" (no right-click there). Next dialog, the two-panel one (after OK) has not types of files field after right-click, see the screenshot "show_matched.png".
Anyway, I ran the modified command:
/opt/slickedit2013/bin/vsdiff -filespec "*" demo real
to exclude possible faults with types of files. And after selecting "Show matching files" Diffzilla treats them matched (it is not true).