I can see this happening on a few shingles during transit or storage IF the plastic strip was not properly adhered to the BOTTOM side of the shingle at the factory.
If this was the case, it could happen in isolated cases when the plastic strip adhered to the tar strip on the top side of the shingle below it when still in the bundle.
Now that is a possibility, but I have never seen it.
If the tar strip is covered by plastic, leaves or other debris, it is wrong and the shingle will never self adhere.
The purpose of the plastic strip is to keep the tar strip from adhering to the shingle above when in the bundle.

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Jim Luttrall
Mr. Inspector.net, Inc.
Allen, Texas 75002