The source for this is a very detailed column written by R. Robin McDonald for the Fulton County Daily Report and published on law.com. I'm simplifying somewhat here for readers and for my own attempted understanding.
Back in 2001, the US Supreme Court issued a decision in a case called New York Times v. Tasini. In this decision the Court ruled on rights of freelance photographers such as Tasini to control or be compensated for works (photos) that were sold for one purpose, such as print, and ended up in an archive later to be used for another purpose such as CD ROM publication.
Now of course the Times wasn't the only entity doing that. Prominently the National Geographic published a CD ROM archive and promptly got itself sued by several people who felt their works had been used in unauthorized and/or uncompensated ways. Because of the locations of these suits a couple ended up being settled in different US Circuits. For this discussion consider the Second and Sixth Circuits
In a 2001 decision known colloquially as Greenberg I (formally as Greenberg v. National Geographic Society I, 244F.3d1267) a panel of the Sixth ruled in favor of photographer Greenberg, holding that the Geographic's archive violated his rights. However, the Second had ruled the opposite way in other cases against the Geographic, basically saying that what the magazine had done was legal and no further compensation was due.
In the normal course of things rulings at the Circuit level stand, even when they're in conflict, until SCOTUS issues an opinion that resolves the differences. In fact, conflicting Circuit opinions are a major factor in the decision to grant review of cases that are appealed to SCOTUS. It's also possible for a full Circuit court to reverse one of its own panels, potentially resolving the difference. The Sixth has not done so, possibly because the judge who wrote the Greenberg I opinion is regarded as something of an expert on copyright law. So far so good.
Now comes the curious case: earlier this month in an opinion informally called Greenberg II (formally Greenberg v. National Geographic Society II, 97-03924-CV) a different panel of the Sixth reversed the earlier panel, pretty much to everyone's surprise. "Curious" is polite lawyerspeak for what you and I might dub "WTF"? WTFF?
First off, the new panel of the Sixth includes a visiting judge from the Second, who wrote the new decision. That's a bit odd.
Second, the rules of the game as it's generally played are that one panel of a Circuit is bound to abide by (and certainly not overtly reverse) previous panels' opinions unless the full Circuit or SCOTUS has something to say on the matter.
Which brings us back around to Tasini. According to McDonald's column (I haven't read the original opinions) the new panel claims to be relying on SCOTUS's reasoning in the Tasini case. If they're right, that case gives them grounds to overturn Greenberg I. But here's where it gets more curious. McDonald quotes several intellectual property lawyers as saying that Tasini really isn't on point here. It's dealing with a separate set of facts. And to make matters even more curious the judge in Greenberg II appears to be relying not on the formal decision of Tasini itself but on explanatory comments (called 'dicta') that the Greenberg II judge feels give "tacit approval" to deciding the case in favor of Geographic.
So what happens now? Well, Greenberg could throw in the towel. It's six years on and he hasn't seen a dime - a 2004 judgement of $400,000 led to the appeal that was decided in Greenberg II. I hate to think how big his legal bills are by now. If he soldiers on there's an obvious appeal to an en banc Sixth and who knows how that will turn out. If it goes against Geographic it seems likely they'd ask SCOTUS for a ruling that would presumably clarify the disparate Circuit views. However, the Court denied certiorari on Greenberg I so they might not take this one, either.