It seems that the Tikal Mirror Manager only checks the id of the features but not their version. This is a problem if the same feature (same id) comes in different versions on the same update site.
Example: EMF
http://download.eclipse.org/modeling/emf/updates/releases/site.xml
Logged In: YES
user_id=245689
Originator: NO
Open a bug at dev.tikalk.com http://dev.tikalk.com/bugzilla/show_bug.cgi?id=2058