appliance not working as intended?

I purchased a philips dehumidifier and I noticed the fan which has three speeds, sometimes automatically goes into full even when in manual mode where the user is supposed to be able to select the fan speed themselves. Sometimes it happens after 5 mins, other times after a longer while, there doesn't seem to be a pattern.

I understand there may be a reason for this, maybe prevent overheating or to make it more efficient, maximizing airflow while the compressor is on and all that. 

The thing is, there is nothing in the manual to suggest any of this and manual mode is supposed to give the user full control. When I called the customer service, they did not appear to know this was a thing. They tested their own machine upon my insistence and confirmed it's the same but can't offer up an explanation. 

It seems like there should be something in consumer law that covers this as it seems like a basic thing manufacturers should make their customers aware of.