Originally Posted by
PeteHski
The only rational explanation is that the presta valve was stuck slightly open. I would replace the valve core if removable.
There is an additional possibility, which is that the tire simply has a slow leak, and it had been significantly more than 24 hours since the person checked it, or inflated it.
I suspect that everyone with a stable of bikes, or who rides infrequently, has this happen from time to time.