Altimeter / Barometer

I own a Instinct 2 tactical. While in the mountains oder while flying i checked the altimeter and barometer from time to time. I noticed that when i am climbing to higher altitude the altitude is increasing as it should, but a the same time the prssure shown from the barometer rises to. The high is always correct when compared to other devices. Normally there should be less pressure when in higher altitude, so how can it be that the barometer shows higher pressure while being higher up the Mountain. Changing the sensor setting didn't vhange a thing.