Nexus7+Androd 4.3+headset+video playback adventures

Some time ago I've purchased a Nexus 7 tablet (the top of the first series: a 16GB model before the 32GB and 3G versions came out).

The main use of the tablet is testing development projects and watching movies on the go by me and playing games by the rest of the family. I love it as it is comfortable in size, easy to use and quick. Although sometimes it's painful to look at the display after the Galaxy S4 (pixels are too large).

Now this wonderful machine got Android version 4.3 (still Jelly Bean). I've upgraded it as soon as possible but did not use it since then. This morning on the first workday after my holiday I wanted to make my daily commute a bit more pleasant by watching a movie (a series episode in fact). Here comes the "but": but it was so quiet that I could not hear the actors’ speech. :O After trying things out for several minutes I figured out that it does not allow raising the volume above 6 on a 0-15 scale. I’ve tried searching on the internet but without any success. In my final desperation I tried the factory reset but it did not fix the original problem (but I’ve loosen a lot of data that cannot be saved to the Google account).

I’ve tried out some more things and while pressing the volume up button on the home screen it finally asked me that do I really want to raise the volume above the safe level? I pressed yes and everything works. #argh

But it should have asked the same thing when I try to raise volume from an application, why does it sets back to level 6 quietly?