My P3 A flies great...however, I'm always getting the wrong altitude when I'm flying and landing. Let's say I fly to 100 feet, I land and the app reading is still at 40 feet. I've calibrated the IMU..three times..all values are correct with that. I've recalibrated compass. Any thoughts? My latest firmware is v1.1.9...the guy at drone shop said don't update firmware as there are issues with latest versions.