Help Bluetooth speaker is turned on when charging my LG G4s

[Android Question]

I have a LG G4s (G4 Beat), and a Harman Kardon SB26 soundbar. The soundbar is paired, and connected to media audio.
Whenever I start charging the phone, the soundbar is activated and put in bluetooth mode.

Does anybody know why this happens? Is there any way to stop this happening without having to disconnect the device?

Thanks