Spotify plays music itself

[tool17]

Plan - Premium
Device - Huawei P9
Operating System - Android 7 Nougat

I play music from spotify through a bluetooth headset. Sometimes, when I disconnect the headset, it after some time runs music itself through the phone's speaker like a phone in my pocket. It happens from time to time, most often when a notification comes (email, sms). I have spotify control turned off on the screen lock, so it's not accidental pressing play in my pocket. Thank you in advance for your help