Generally improper install. The carpet may not have been power stretched.
When you add moisture fibers swell and push against each other and with no where to go but up which is the least resistance.
It can be frustrating. Maybe include it on some leave behind literature as a possibility on carpets that are denser and may not have been power stretched.
This way it was proactively spoken about before it happens. As far as a resolve to it, airmovers, HVAC helps if really concerned and dehumidifier aids greatly in removing the moisture in the air.