Volume buttons not working after waking from sleep

[0007776]

So I'm assuming this is a software problem although I guess it could be a hardware issue just starting. Whenever my computer wakes up from sleep the volume icon in the top is greyed out and the volume buttons don't work to change the volume. If headphones are plugged in the volume control works for them, and a restart fixes it for the built in speakers until the next time the computer sleeps.

I'm attaching a screenshot so you can see what I'm talking about.

 

[0007776]

So after a couple days it has apparently fixed itself and is working consistently now. But in case it comes up again I'd still be interested in knowing if anyone has ideas as to what the problem was.