JBM,
Don't know about the apparent contradictions - I assumed the poster was referring only to those bees without pollen loads? But, from the earlier suggestion that brooding was still ongoing, I would be wondering (if brooding was considerable, and open) where the larval water content might be sourced. Likely water collectors needed in abundance? Or maybe there is some nectar collected (never say 'must') for brooding? Needs some thought to connect the observations, perhaps? Or even more observations to confirm, rather than jumping to conclusions?