I tried Nitro's advice and it worked flawlessly. Listed here (in case this saves time, or is clearer);
1. Search "Services" or Locate: Control Panel> Administrative Tools> Services
2. From there, scroll down to the find "Human Interface Device Access"
3. Right click on it
4. Open properties and verify it's startup type is set to automatic, and then make sure you click OK or apply.
5. You're done! Click your volume icon to verify it worked.
Its really simple fix and it worked for me. it should take about 30 seconds to fix.
For some reason my volume bar stopped opening and i had to use my keyboard volume keys or my remote to change the volume because whenever i clicked on the icon, in the task-bar, nothing would happen. I opened services and changed HIDA to startup automatically, and everything was back in order.
As far as your windows not recognizing the buttons, but ubuntu is, maybe check to make sure your windows has full driver support plugged into the computer and be sure that ubuntu isnt defending/protecting/locking windows from using it. There is a chance that ubuntu has claimed ownership of it and has put a foot print or lock or benchmark, for lack of better words, on the keyboard itself that prevents other systems from taking control of it. Maybe if you took the name away from the keyboard and gave it something different, than the factory name, maybe somehow ubuntu might loosen up on it and allow it to crossplatform. On the other hand, it might still reclaim ownership after the identity has changed.
If you had to install drivers for ubuntu, uninstall them and the ones for windows (if you installed the drivers for win) and then reinstall the drivers for windows first, THEN install the drivers for ubuntu. Hopefully windows will try to claim ownership like ubuntu did, and ubuntu, being its own independant os who dont need to rules, will disregard that and use it with what you could theorize as a temporary license. This is all just theoretical and possibly really dumb, but i feel like it has potential. Ownership problems usually come from what was first and what has more authority/ freedom. There are 3 options in this driver install predicament. A. Drivers on no OS, see how that goes. B. Drivers on Windows first and if it doesnt work naturally on ubuntu, install drivers then. or C. Install drivers on Ubuntu first, not windows, and windows has no idea about the keyboard yet, then if the keyboard doesnt work naturally on windows (which it probably will considering it's made by windows and you're using a windows OS), THEN install the drivers on windows. At one of these points, the formula should allow both the ability to interprit the keyboard without obstruction. It will definitely take time and trial and error, but one of these 3 should definitely be the solution. If not, you will need some ubuntu software to help you out, or windows. I'm doubtful windows is causing the problem as i im guessing with windows you are getting a plug and play result from it.