Yep...I highly suspect that this is a case of "natural vulcanization" ( a term I just kind of made up...but it works) When tires roll on the ground, they create heat which in turns causes a natural bonding between the rubber in the tire casing and the rubber in the tube. Add in the fact that there are natural rubber binders in the tire casing, condensation, and heating/cooling cycles, over time they will bond. One way to keep this from happening is to add a light layer of talcum powder on the inside of the tire when you install it and the tube. Also, this will allow the tube to move freely of the tire while riding. It's a technique that mechanics have used for years. Tubular tires are built the same way, for the same reasons. And, just for information sake, your tube patch kit works the same way, although the glue causes a chemical reaction that does the same thing, quickly.
That being said....you never really know what is going on in someone's brain...they may have actually glued the tubes in!!!!!!! lol
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Droping the hamer since '86