Created attachment 108719 [details] picture of dropdown menu with Raise maximum volume option Steps to reproduce: 1. Open the dropdown menu in the volume control as shown in the screenshot 2. Set it to "Raise maximum volume" 3. Reboot Kubuntu 17.10 4. The volume control reverts to only having the default option checked and the maximum volume is not "raised" anymore.
That's intended, this is only temporary raise of maximum volume. To make it permanent, you need to use global maximum volume option.