1. Play a song.
2. Change the volume to -10 dB

Now, the volume decreases as expected.

3. Go "next".

What happened:

The volume got reset to 0 dB. However, if you go to the volume setting again, you will find it still shows "-10".
If you change it up or down (i.e. to -9 or -11), it will be re-applied (i.e. your volume will actually go down no matter what, since it was 0 dB due to bug).

I'm playing m4a (AAC) audio files withour RG info (nor is RG enabled), for what it matters.