Condensation under mattresses

This past weekend we took our brand new hybrid out for the first time. We had a bit of rain, so I was super vigilant, looking for any leaks. The tenting and seals all made out great, but I was a bit startled, because in being thorough looking for leaks, I removed the mattresses and felt wettness on the bottom of the mattress, as well as the bunk-board. This was the same on all 3 of our tip-outs. The following night, one of the kids was scared and slept with us, so no one slept in that tipout; consequently, no dampness under that mattress but condensation under the mattresses where people slept. I was spooked at first, fearing leaking, but it became quite evident that this was just condensation. The overnight low was in the low 40's so I suspect the body warm through the mattress meeting the cold air underneath the bunks =condensation.
... is this a common thing? Anyone else want to pitch in with their experience on this? The user manual talks about condensation as one might typically find it, on the tenting, but I was surprised to find it under the mattress.