Recently I knew a molecular biologist postdoc who was upset since she was placed by her boss as a second first-author in a paper that she wrote from scratch. Her boss put a bioinformatician/biostatistician as the first first-author, with a reasoning to the postdoc that she would not have anything if they take out the data processing part.
And it turned out that she is not alone. From this postdoc's facebook, I learned that some of her friends admitted that they also experienced a very similar situation: being a molecular biologist, did all the lab work, wrote the paper, but put as a second author while the first one is a bioinformatician.
Apart from politics in the lab etc., I wonder if this is really quite common. If it is, don't you think it's quite unfair for the molecular biologist?