As I said, probably down to the vari-pitch lathe which tries, depending upon the dynamic range of the music, to pack record grooves as close together as possible. If it’s not set up correctly, one groove impacts on another or, in extreme cases, one runs into another and you have to start again.

There was one story, I think it had something to do with Monty Python, where the client wanted to put both sides of a record on the same side so the listener didn’t know which would play when the needle was dropped; i.e. concentric spiral grooves. The vari-pitch tried to pack them together whilst the operator tried to override the thing to leave room for the other side between them.