Beatles magical mystery tour on sansui amps simulated synthesized surround mode

[aifrecords]

i have non quad magical mystery tours on vinyl, first is original master mobile fidelity sound lab,next stereo copy, just tested side one on both and weird thing is drums cut out on hello goodbye and other songs on both copies, and some other instruments drop out as well, why is this happening? weird , its on the synthesized 4 channel mode on the amp.

on dark side of the moon master copy vinyl some instruments are very faint on this mode as well...