What makes an app unique from POV of options -> assign to desktop?

What is the set of things that differentiate one application from another from the point of view of right-click on dock icon -> Options -> Assign To (All Desktops / This Desktop / None)?

I've experimented and haven't been able to hit on a combination of actual binary name / Info.plist values / PkgInfo string that will make Mac OS X workspaces think a duplicated application is different from the original for purposes of automatic desktop assignment.