Using "-" for "previous branch" failing with rebase

I recently learned that there are several places where git allows use of "-" to refer to the previous branch, e.g.

  git checkout -b dev
  # hack, hack
  git checkout master
  git merge -
  git checkout -

However, it doesn't seem to understand "-" in the context of a rebase:

  git checkout branch_a
  # hack
  git commit -a
  git checkout branch_b
  # hack
  git commit -a
  git rebase -         # I'd expect to rebase onto branch_a

but I get

  fatal: Needed a single revision
  invalid upstream -

Issuing

  git rebase branch_a

does exactly what I'd expect (as "git checkout -" puts me on "branch_a").

Is this just an interface inconsistency or is there a some technical reason this doesn't work (or, has it been addressed/fixed, and just not pulled into Debian Stable's 1.7.10.4 version of git)?

Thanks,

-tkc