Vocal Isolation of Pink Floyd's Flaming

This video lets you hear Syd Barrett's lead and backing vocals on their song Flaming from Piper at the Gates of Dawn. Pink Floyd are well known for including lots of "Easter Eggs" in their songs where messages are hidden in the audio if you play the song backwards or use Out of Phase Stereo techniques. But I had never noticed the backing vocals on one of my favourite early Floyd songs have different lyrics.
I hear the lead vocal saying "Yippee you can's SEE me" but the backing vocal says "Yippee you can't HEAR me".
Was it done on purpose? An honest mistake?

[@twcc406]

Love it, well done that man ... was always aware the lyrics had an odd sound, now it is so obvious why !!