Plastic strip on the back of Shingles...

AFAIK after shingles are installed, the heat from the sun melts the plain bitumen strip on the front and back to stick the overlapping layers together.
My question is: Why is the strip on the back covered with a thin plastic cover marked (in many languages) "DO NOT REMOVE"? Does this melt before the bitumen melts? what is the effect of removing the plastic cover strip? (it must be important otherwise they wouldn't have written it in so many languages...)
A worker was installing them at our factory and removing the strips until I told him what the writing meant. He said that the seller told him to remove the strips!
TIA for any (useful!) replies!
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Abdullah Eyles wrote:

Probably not to be removed before installation? I would imagine the supplier would know what they were talking about.
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Then they would write "Remove before installation", IMHO...
In that case it would stop the sheets sticking together during transit, but there is a deeper meaning, I am sure...
(Unfortunately the sellers here don't know much about what they sell - not like UK.. or maybe like B&Q??)
Any ideas?
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