Temporary altitude increase on mode change

I just upgraded an Iris+ from 3.5.5 to 3.6.9 (ChibiOS). In test flights after an auto tune I noticed the motors would rev on mode switches. Switching modes repeatedly causes the aircraft to climb a foot or so with every switch. Afterwards it gradually descends to the proper altitude. Log at https://drive.google.com/file/d/13jFcdjkUIvUUCkwwdrX_1uNV2ISeoKoT/view?usp=sharing