I have regularly multiples in the "By This Artist" window on my iPad and in my "Album" window of Control:PC after selecting an artist (not after selecting a composer!).
After reseting my MC200 (with or without resetting my TwinStore) they disappear, but will come back again.
I have an MC200 as source and core and a TwinStore as store.

living: 218, 2x DSP5200SE, 1x DSP3300
study: 218, 2x DSP3200
sleeping: 218
spare: HD621, AC11, DSP33C