So to follow up on this matter, as of today our controversial Comment is indeed under review at BMC Research Notes. Hooray! (And thanks again to Ged for the suggestion).

Something interesting I learned in the process that may be worth sharing:

BMC was concerned that our re-use of data published in the criticized paper would violate copyright of the original paper's publisher, so we would need permission for our re-use. I do disagree with that, because of the obvious Fair Use nature of our Comment and also because we are only using the same image data, but not entire figures from the original paper. Much like you can use the "Lena" image without asking permission from anyone else who's used the same image in their paper before.

But that is not the interesting point - the interesting thing I learned is this: the original paper was published in an IEEE journal, and as an IEEE member, one of my membership benefits is that I can get permission for re-use of any IEEE-copyrighted materials for a processing fee of, hold your breath, $3.50.

You may of course think of copyright and licenses and copyright transfers to journals what ever you will. But I think that's kinda cool, especially that it took literally 5min to get the re-use permission online rather than argue with BMC over the merits of our Fair Use defense.

Now let's hope BMC is asking people for reviews of our Comment who actually understand the subject matter...

Cheers!
  Torsten