I don't know what could have caused this.
LOL. I read years ago that some recording studios used to install a "producer's strip" - not connected to anything - on their recording consoles to keep "interfering" producers' fingers happy tweaking the mix.
IIRC there was a documentary about the Beach boys a few years ago, where they claimed that the record studio did exactly that to let the Wilson brothers dad "twiddle" with the dummy mixing board so he *thought* he was tweaking their sound, just to keep him happy...