I have an album called Rogue's Gallery which consists of two CDs named like this (cut and pasted from SqueezeCenter): 


Rogue's Gallery (Disc 1 of 2)
Rogue's Gallery (Disc 2 of 2)


I can only add the first one to favorites.  Same situation with both the SqueezeBox3 remote and SqueezeCenter WebUI.  SqueezeCenter seems to think the first disc is the same as the second one as far as favorites goes and won't add it.  When I remove Disc 1 and try to add Disc 2 as a favorite, it still makes Disc 1 the favorite instead.  I am able to play both discs okay however.

From looking at bug# 10259 it seems the album name is used as the identifier; perhaps the uniqueness/already-in-favorites check is only looking at the first 16 characters or doing some other partial comparison instead of looking at the full name.

As an aside I selected "Infrant RAIDiator 3" in the OS above; however my ReadNAS NV+ is actually running RAIDiator 4.1.4 but there is no selection for RAIDiator 4 available.