Should co-first authors be listed in alphabetical order? The field of research is the biological sciences.

Graduate student B worked on the project for 2 years: he did experiments to gather genome-wide data and analyzed part of that data. He defined the direction and feasibility of the project, and developed the methodology; if it were not to him, there wouldn't be a paper.

Post-doc A picked up the project for 1 year after graduate student B left the lab, analyzed the data, wrote the paper, contributed 4 key figures (exactly half of the figures) and at least half of the scientific conclusions. 

It was agreed upon that A and B would be co-first authors, but currently they are listed as B, A, et al. 

Do you think A would be entitled to feel some kind of injustice at not having his name listed in alphabetical order? Is there a consensus that co-first authors should be in alphabetical order and is the editor likely to point this out?

[edit] Additional information: 
In this field, you can specify 'co-first authors' at the time of submission, and it is written as such under the author's list on the final publication as "X an Y have contributed equally to this work". Which of course is a big source of conflict.

Thanks :)
I don't see any way to view this other than as a misunderstanding or miscommunication.  (Not necessarily an innocuous misunderstanding: perhaps someone is trying to pull a fast one of some sort.)   

I am a mathematician, so maybe I am especially sensitive to logical issues, but I can't think of a situation in which someone tells me something that sounds like a logical contradiction in which I wouldn't just say, "I'm sorry: I must be confused because that sounds contradictory.  Could you please explain it again?" 

My only guess at the resolution of the contradiction is that someone is in fact trying to change their mind about the ordering of the authors.  I know little about the conventions and nuances of author ordering (because in pure mathematics the order is almost always strictly alphabetical), but I do think I understand the meanings of all the terms involved, so I can only imagine that if you submit a paper to a journal saying "by Bravo, Alpha, Charlie....Please note that Bravo and Alpha are co-first authors" then the editors will respond by calling attention to the contradiction.  What else?