From http://api.jquery.com/jQuery.when:

If a single Deferred is passed to jQuery.when(), its Promise object (a subset of the Deferred methods) is returned

For consistency, we should always create a new master Deferred.

We follow through, but the code—both ours and library consumers—is more complicated than it needs to be as a result. The upcoming major version bump is a chance to unify single- and multiple-argument calls to jQuery.when, if we agree that doing so is valuable. (we did not)