Volume decrease button not always working

[Wastelands]

Volume down button not always working. It seems to be software problem. I've closed all apps in bg and suddenly it started to work. I happens every day.

 

[Wastelands]

It happens with Windows Phone 8.0 however I have developer preview program and installed some updates unitil 8.1 (stopped here, because want to have device with 8.0 for tests)