I'm really liking this scenario:
When you say you inflated the tires up to 80 psi prior to the ride, I’m wondering if that amount of pressure was insufficient to (re) mount your 5000TL’s fully. What I’m wondering is this: when you don’t ride your bike for a week or so and the tire gradually deflates lower and lower, the bead sort of pulls away from the rim shelf. When you use your foot pump to take it back up to 80 psi, the pressure is building back gradually and it might appear that all is well and that there are no leaks.