If [MENTION=135358]xenologer[/MENTION] is correct, I wonder if letting the air out of the tube after mounting, and then pumping it back up to full pressure would allow the tube to redistribute itself and avoid the stretched-out parts. This shouldn't cause a pinch if you were careful enough to avoid trapping the tube under the tire bead the first time around.

From the pictures, the bulged punctured areas look so much like the tubes were allowed to penetrate the spoke holes, that it's really perplexing for this to have happened with double rim tape. Hats off to you, [MENTION=429363]DQRider[/MENTION], for attempting to control as many variables as you can in this investigation.

To [MENTION=362748]SquidPuppet[/MENTION]'s point, a narrower rim tape like 10mm Velox should cover up all of the spoke holes completely and not interfere with the bead seating at all. Something to consider.

Perversely (?), I'm tempted to pick up a wheel or two with these rims and see if I can replicate the issue for myself.