Ouch... just while reading that post iTunes in shuffle mode decided to play "Just around the corner, half a mile to heaven"...
Never seen anyone paper over the plate... but the bathroom light switch was held in place by 4 layers of paper between device and plate, just with a small cutout for the rocker. Removing the wallpaper was promptly followed by the switch falling out.
Common problem with old work - the steel boxes were slightly bigger in diameter, so from about the 1960s onwards the claws on devices didn't spread far enough to secure the device. And for some reason most electricians were too lazy to use screws.
With the advent of the first PVC boxes screws became more or less useless because they didn't go into the box itself but a thin PVC ring that was just snapped into the box... pulling a bit harder on a Schuko plug reverses that process...
So, it's very important to have boxes solidly plastered in from all sides, so the clamps can't spread the PVC box.
