Jason is correct! My Walter / Mahler 9 / Columbia record set has each movement occupying its own side, so it has nothing to do with fitting the length of movements!
Movements 1 and 4 are on the first record, and 2 and 3 on the second record.
This was done for convenience on stacking auto-players, but is inconvenient for everybody else. I notice that noise is significantly worse on the first record, probably because it has been removed from its sleeve twice as often. It had been in paper sleeves with a plastic liner until recently when I swapped the sleeves for anti-static ones by Nagaoka.
Mahler himself was sometimes unsure about the best order for his movements.
I am one press of a button away from ordering my next purchases from Presto. Because I love Bruno Walter's performance of the 9th so much, I have included a CD copy by Alto of my record set, which also includes Reiner conducting #5. Under A$17.
I discovered there is an earlier Walter performance recorded in Austria just before Hitler merged Austria into Germany. The performers are mainly Jewish. Naxos CD, about A$20. Then I added a five CD set from Warner of Barbirolli conducting #1, #5, #6 and #9 for under A$20 the lot!
There will be some vinyl in my order as well ...

