Yeah, I've never heard a volume drop either, but it sounds like a) the OP is listening to a specific, non-standard version [or possibly corrupted file?], or b) is just hearing a "volume drop" based on the apparent volume principle-- a single or solo'ed-out instrument will sound louder than a group of instruments together; an acoustic guitar and vocal track, if back-to-back with a mixed band track, will sound louder than the full band track ("apparently"... it's an audio-illusion, the VU meter might show no real difference, but the ear will hear a difference).
GJ