I've lost volume control after updating to LMS 7.8

I just updated from 7.6.1 to the current version of LMS 7.8 because album art had ceased to show up on the main page in iPeng 7. The update fixed the art problem, but now I have no control over volume. Volume is stuck at a reasonable listening level, but volume sliders don't work at all now - not on LMS on my laptop, in iPeng, or in Logitech's own Squeezebox controller. Can anyone offer advice?

I'm running LMS 7.8.0 - 1395310205.

Thanks in advance!