This happens only when the options panel is initialized. If a sound pack has a custom maximum volume set (that is not 1) on a certain sound, its slider still has its maximum set to 1. This prevents using a value higher than 1 when changing the volume.
Workaround: Change to the default sound and change back again. This should correctly apply the maximum value on the slider so you can change it. This has to be done every time the options panel is reloaded (every time a mod is enabled/disabled and after a restart).
This happens only when the options panel is initialized. If a sound pack has a custom maximum volume set (that is not 1) on a certain sound, its slider still has its maximum set to 1. This prevents using a value higher than 1 when changing the volume.
Workaround: Change to the default sound and change back again. This should correctly apply the maximum value on the slider so you can change it. This has to be done every time the options panel is reloaded (every time a mod is enabled/disabled and after a restart).