Mouse volume up/down buttons press B/C in game ??

Hi,

I have a Naga left handed edition. I have mapped 2 of the buttons to volume up and down.

When playing Apex Legends, pressing those buttons changes the volume but also triggers the in game aciton for the keys B and C. This only happens with the mouse, not when I change volume from my keyboard or headset. It does not matter which mouse buttons are mapped to volume control, they all do this.

If I change the bindings from B and C to other keys it goes away.

I cannot understand why Apex Legends understands the mouse buttons for volume control as also being B/C. Does anyone have any idea?