Dropbox supports two types of 3rd party apps each with different file permissions. 1) Sandbox, and 2) Full Access. If you jail by registering a "Sandbox App", you give up the ability to share/collaborate in a directory with other Dropbox users. To have a third party project that provides sharing you must abandon the "Sandbox" permissions and instead request "Full Access" - which means you get a token that give you access to the users entire dropbox directory. I have several email threads with the Dropbox team discussion this issue at length. Perhaps this has changed since I was neck deep in this issue but I don't see anything in their changelog to suggest that.

Ah, wasn't aware of that.