If you use VLC Media Player to play the songs, you can reverse the channels on playback by clicking audio/audio channels/reverse stereo.
I tried this both with the downloaded Beatles Flac file and then with the Flac converted to mp3. Both played correctly in VLC Media Player when I reversed the channels.
Don’t have a clue as to why this happens but it seems to address your issue.
If you use VLC Media Player to play the songs, you can reverse the channels on playback by clicking audio/audio channels/reverse stereo.
I tried this both with the downloaded Beatles Flac file and then with the Flac converted to mp3. Both played correctly in VLC Media Player when I reversed the channels.
I tried it with the FLAC file (originally and again now, both times with VLC), and it sounded fine the normal way (no voice in background and the instruments seemingly balanced with it).
Now, I tried the "reverse" of it, just to see what would happen (when I read your post) and the voice does seem to be in the background and out of balance with the instrumental part, when it's reversed for me.
I'll give you the one song I tried, "Please Please Me" (the song on the album by the same name, too). The voice is on the right channel when I played it normally. And when I reversed it, the voice was on the left channel and seemingly faded into the background.
I'm assuming that the normal configuration is for the voice to be on the right channel. Is that the normal configuration for you? (whomever wants to answer this one)...
And..., I'm using that downloaded FLAC file[s] downloaded that I specified up above.