I've seen it discussed. According to one news article, the bullet was in the custody of an investigator, and that might not have been the appropriate chain of evidence. They know who had it, I guess the question is whether the investigator was authorised to be a courrier for evidence or not. The implication is no, and I don't have the ability to check the records in texas to see if he was or not.
They are not arguing that the doctor didn't examine the bullet, just that the bullet that was tested the next day might not have been the one pulled out of the guy (however, the doctor did not suggest that the bullet tested looked different from the bullet he pulled out, and remember the testing didn't prove the bullet came from the guy's gun according to the evidence presented in this story -- if they were REPLACING the bullet with one fired from the guy's gun into gell (as suggested in this story), you'd expect it to definitively match the gun.
But since testimony was to be given that the bullet hit bone in the other leg, they had to shoot it into a cadaver, as the feds are well known to do, from the Klinton days.