Upon launching the game, the music in the main menu is relatively low, until settings are applied in the options menu (notably the Video settings). After applying changes, the music volume increased to its actual setting.
How to recreate:
1. Seemingly, just launch the game
2. Music Volume will be lower than the actual setting (here, 100)
3. Make changes in the video settings, and apply them
4. Music Volume will return to its actual setting