Don't know if this is by design but if multiple devices add one or more different profiles and then sync with the same desktop server, duplicate collection numbers are created.

For example, an iPad and an iPhone are both synced with a server.  Then the iPad adds movie ABC and it is assigned collection number 435.  If the iPhone adds a different movie (DEF), it is also assigned collection number 435.  If both devices sync with the server, both ABC and DEF are uploaded and they both will have collection number 435.