I think I found a software bug. Hope you can help me

My configuration:
- 42PFL7606K/02
- Using the headphone port to get the sound to external hifi-system

While I'm using the TV, im switching between one HDMI device an the internal DVB-S tuner. The TV is plugged off over the night (guess that's important to know). I noticed that sometimes, switching between HDMI and SAT, the sound level on the headphone port is really low -> even turning the hifi-system to max level is still really quiet.

I found the following procedure to replicate the problem:

  1. Power on the TV
  2. Switch to SAT tuner (DVB-S)
  3. Power soft off the TV (by remote control)
  4. Power hard off the TV (use the power switch)
  5. Power on the TV
  6. Sound while watching SAT is really low
  7. Power soft off the TV (by remote control)
  8. Power on the TV
  9. Sound is now back to normal

Is this is a software bug or am I doing something wrong?