Yes, I've tried all without results.
Because the problem is only in two activities I've compared with more attention both codes and finded that the problem is caused by following code:
Sub Activity_KeyPress (KeyCode As Int) As Boolean
If KeyCode = KeyCodes.KEYCODE_BACK Then
audioBg.Stop
Activity.Finish
End If
Return True
End Sub
Disabling this audio volume buttons works properly.
It's the first time that I program software from scratch, maybe I wrote this not in the right way.
There's a way to prevent this in Activity_KeyPress?