How do you solve a problem [of] Gustav?

Here, from the proceedings of the 16th "Mahlerfest" in Boulder, Colorado (8-12 Jan. '03), is a presentation by Jeffrey Gantz on Mahler's 6th. This piece, by Mahler fanatic* Gilbert Kaplan, too, deals with the same subject, albeit in a less-specialist manner (as usual, NYTimes registration required). I'll quote first from Kaplan,

A controversy has raged since 1963, when a new edition of the Sixth was published, reversing the accepted order of the movements. Some musicologists objected to the change for lack of evidence, but since the edition was approved by the society, it has been followed by almost all conductors. (One notable exception has been Simon Rattle.)

Now it has become clear that the transposition of movements was no mere mistake but a willful act of an editor, Erwin Ratz. As it turns out, Ratz distorted the facts and withheld evidence contradicting his opinion that according to musical theory, there could be only one correct order, Scherzo-Andante.

For those inclined, here is Gantz:

In 1963, the Critical Edition of the Sixth came out from the IGMG, and lo and behold the Scherzo was back in its original second position, Erwin Ratz explaining that some time before his death Mahler had changed his mind. Ratz provided no evidence for this statement; he didn't even cite Alma's telegram. Nonetheless, few conductors challenged his edition. John Barbirolli continued to perform the piece with the Andante preceding the Scherzo, but when his recording appeared, EMI switched the movements (apparently without his approval) to conform to the Critical Edition. (In the most recent release of this performance, in its Double Forte series, EMI has reswitched them so they're back to the Andante/Scherzo order Barbirolli favored.) Harold Farberman, from 1950 to 1963 a BSO percussionist, stuck with the Andante/Scherzo order on his MMG LP with the London Symphony in 1982; when Vox released this performance on CD in 2000, however, the label switched the movements to conform to the Critical Edition (here again the conductor was not consulted). Benjamin Zander's first performance with the Boston Philharmonic (briefly available on tape in the mid '80s) had the Andante preceding the Scherzo, but on both his 1994 live BPO recording and his 2001 Philharmonia effort, he's reverted to the Critical Edition. Simon Rattle has been the most outspoken advocate of the Andante/Scherzo order, and his 1989 recording of the Sixth has become the whipping boy of uninformed reviewers.

This, though, isn't quite the point. Well, maybe it is: it depends on how "in to" Mahler you are. I'll lay my cards down and say that I prefer Scherzo-Andante, as it has both a "more 'modern'" sensibility, and it makes the final movement even more devastating than it is on its own. There. No, the overarching point, then, is this: in the absence of a clear textual tradition, what are we to do? Erwin Ratz might be the dastardly scoundrel here, but who's to say that Mahler wouldn't have revised it again? And again? And again? And so on. He died relatively young, so another twenty years could have both carried forward the direction in which he seemed to be starting with the 10th (as we can plainly see from the completed four-stave draft) and brought serious revisions to his symphonies. We don't know.

Mahler, then, provides something beyond which Wagner (or almost anyone) does. We know what Richard Wagner wanted. Indeed, we know down to the details (including acoustics and staging) what Wagner wanted. That's part of the game of music-dramas, though. Symphonies and other works, well, no one ever gives it as much consideration. There's no illusion to create: the orchestra is obviously playing the music and that's all they're doing (more or less). Mahler didn't help matters by not quite knowing what he wanted. Frau Mahler-Gropius-Werfel added to the confusion by pulling a Constanze Mozart and divining her dead spouse's wishes for decades after his death. What do you do?

I don't know, but I think the answer is pretty simple. You go on. In the case of the 6th, you pick an order to the movements, justify it (or not), and perform it. Eventually, I think - or hope - the experts and the "experts" will sort things out and arrive at either the "right" answer or the right answer. Until then, it's simply essential to do the fundamental business of music - make it. Everything else is details.