I’ve just realized that this isn’t an isolated problem–there are a number of similar problems. So far, this is what I’ve come up with in the John Gardiner set of Bach Cantatas. The following discs all show up as Artist=Bach instead of Gardiner:
Vol. 4, disc 1 (but disc 2 is correct)
Vol. 9, disc1 (but disc 2 is correct)
Vol. 15 (only one disc)
Vo. 16 (only one disc)–this one’s really weird, because it created one disc under Gardiner with just the 1st track, and a 2nd disc under Bach with tracks 2-26
Vol. 21, disc 2 (disc 1 is correct)
Vol. 22, disc 1 (disc 2 is correct)
Vol. 23, disc 1 (disc 2 is correct)
Vol. 24, disc 1 (disc 2 is correct)