Unable to switch music to other devices when using bluetooth headphones

[VadimKraev]

I'm a free plan user using an iphone with the latest iOS (not beta) and can seamlessly switch music between my PC (Windows 10) and the phone without any problems when music is played through phone's dynamics. 

But when I turn on my bluetooth headphones (Marshall Major 2) the music automatically switches from PC to the headphones and then I just cannot switch it back to any other device like a PC. The app doesn't show me the Spotify Devices Menu but shows the iPhone Devices Menu instead (screenshot attached) where i can switch only between iPhone and headphones. To be able to switch the music back to PC I first need to turn my headphones off, then I can see the needed Devices Menu (But even then I sometimes don't see other devices on that menu and have to relaunch the app to fix it).

Am I doing something something wrong or is it a bug or something?