I think the reason is the first one is for the Admin view of the VDC (as that was directly requested). The second one (although is for AdminVapp) is going to return the normal VDC view as a Vapp has a normal VDC. The Admin View of a VDC has different data and functions available to it.
What I have done in this situation is taken the GUID part off and then rebuilt the URL I needed, based on the functions I wanted to perform. (As they are the same GUID, just a different path and rights model to each)
Also something I see, you might want to setup your public addresses section in vCloud if you have not (for testing should not cause issues, but without it some functions will return odd url's)