Could also be an "IMPORT" - some machines had a plastic rather than glass - a sheet of glass was then placed in front of this. It prevented breakage during shipping.

If the machine has a 240V input with NO step down then this could be the reason - is the back sheet glass or acrylic?
 My BANK A BALL has the same thing except clear sticky tape was used to keep the two together - this just crumbled off though - no issues at all removing it...

...OR.. could be as Tony suggests