I have the same set-up than you have: iMic through a USB Hub that goes to sleep with the Carnetix P1900. The volume stay where is was before going to sleep, but I had a similar problems with system preferences being change.
I had a radioSHARK and iMic (both from GriffinTechnology) on the same hub. After waking-up, the sound input would had switch, sometime, from iMic to radioSHARK. I wrote to Griffin and they ask me to check if my HUB was backward compatible with USB 1.1 (or 1.0, I don't remember). It was so, so I move the radioSHARK to another hub and the problem disappear.
It could be many others reasons, but you could start by looking at your accessory.